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Pessatti, Tomás, Hernán Terenzi und Jean Bertoldo. „Protein Modifications: From Chemoselective Probes to Novel Biocatalysts“. Catalysts 11, Nr. 12 (30.11.2021): 1466. http://dx.doi.org/10.3390/catal11121466.
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Chemical reactions can be performed to covalently modify specific residues in proteins. When applied to native enzymes, these chemical modifications can greatly expand the available set of building blocks for the development of biocatalysts. Nucleophilic canonical amino acid sidechains are the most readily accessible targets for such endeavors. A rich history of attempts to design enhanced or novel enzymes, from various protein scaffolds, has paved the way for a rapidly developing field with growing scientific, industrial, and biomedical applications. A major challenge is to devise reactions that are compatible with native proteins and can selectively modify specific residues. Cysteine, lysine, N-terminus, and carboxylate residues comprise the most widespread naturally occurring targets for enzyme modifications. In this review, chemical methods for selective modification of enzymes will be discussed, alongside with examples of reported applications. We aim to highlight the potential of such strategies to enhance enzyme function and create novel semisynthetic biocatalysts, as well as provide a perspective in a fast-evolving topic.
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Jarrell, Ken F., Gareth M. Jones, Lina Kandiba, Divya B. Nair und Jerry Eichler. „S-Layer Glycoproteins and Flagellins: Reporters of Archaeal Posttranslational Modifications“. Archaea 2010 (2010): 1–13. http://dx.doi.org/10.1155/2010/612948.
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Many archaeal proteins undergo posttranslational modifications. S-layer proteins and flagellins have been used successfully to study a variety of these modifications, including N-linked glycosylation, signal peptide removal and lipid modification. Use of these well-characterized reporter proteins in the genetically tractable model organisms,Haloferax volcanii, Methanococcus voltaeandMethanococcus maripaludis,has allowed dissection of the pathways and characterization of many of the enzymes responsible for these modifications. Such studies have identified archaeal-specific variations in signal peptidase activity not found in the other domains of life, as well as the enzymes responsible for assembly and biosynthesis of novel N-linked glycans. In vitro assays for some of these enzymes have already been developed. N-linked glycosylation is not essential for eitherHfx. volcaniior theMethanococcusspecies, an observation that allowed researchers to analyze the role played by glycosylation in the function of both S-layers and flagellins, by generating mutants possessing these reporters with only partial attached glycans or lacking glycan altogether. In future studies, it will be possible to consider questions related to the heterogeneity associated with given modifications, such as differential or modulated glycosylation.
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Chang, Yie-Hwa. „Impact of Protein Nα-Modifications on Cellular Functions and Human Health“. Life 13, Nr. 7 (24.07.2023): 1613. http://dx.doi.org/10.3390/life13071613.
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Most human proteins are modified by enzymes that act on the α-amino group of a newly synthesized polypeptide. Methionine aminopeptidases can remove the initiator methionine and expose the second amino acid for further modification by enzymes responsible for myristoylation, acetylation, methylation, or other chemical reactions. Specific acetyltransferases can also modify the initiator methionine and sometimes the acetylated methionine can be removed, followed by further modifications. These modifications at the protein N-termini play critical roles in cellular protein localization, protein-protein interaction, protein-DNA interaction, and protein stability. Consequently, the dysregulation of these modifications could significantly change the development and progression status of certain human diseases. The focus of this review is to highlight recent progress in our understanding of the roles of these modifications in regulating protein functions and how these enzymes have been used as potential novel therapeutic targets for various human diseases.
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Sheeran, Freya L., und Salvatore Pepe. „Posttranslational modifications and dysfunction of mitochondrial enzymes in human heart failure“. American Journal of Physiology-Endocrinology and Metabolism 311, Nr. 2 (01.08.2016): E449—E460. http://dx.doi.org/10.1152/ajpendo.00127.2016.
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Deficiency of energy supply is a major complication contributing to the syndrome of heart failure (HF). Because the concurrent activity profile of mitochondrial bioenergetic enzymes has not been studied collectively in human HF, our aim was to examine the mitochondrial enzyme defects in left ventricular myocardium obtained from explanted end-stage failing hearts. Compared with nonfailing donor hearts, activity rates of complexes I and IV and the Krebs cycle enzymes isocitrate dehydrogenase, malate dehydrogenase, and aconitase were lower in HF, as determined spectrophotometrically. However, activity rates of complexes II and III and citrate synthase did not differ significantly between the two groups. Protein expression, determined by Western blotting, did not differ between the groups, implying posttranslational perturbation. In the face of diminished total glutathione and coenzyme Q10levels, oxidative modification was explored as an underlying cause of enzyme dysfunction. Of the three oxidative modifications measured, protein carbonylation was increased significantly by 31% in HF ( P < 0.01; n = 18), whereas levels of 4-hydroxynonenal and protein nitration, although elevated, did not differ. Isolation of complexes I and IV and F1FoATP synthase by immunocapture revealed that proteins containing iron-sulphur or heme redox centers were targets of oxidative modification. Energy deficiency in end-stage failing human left ventricle involves impaired activity of key electron transport chain and Krebs cycle enzymes without altered expression of protein levels. Augmented oxidative modification of crucial enzyme subunit structures implicates dysfunction due to diminished capacity for management of mitochondrial reactive oxygen species, thus contributing further to reduced bioenergetics in human HF.
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Bond, Michelle R., und John A. Hanover. „A little sugar goes a long way: The cell biology of O-GlcNAc“. Journal of Cell Biology 208, Nr. 7 (30.03.2015): 869–80. http://dx.doi.org/10.1083/jcb.201501101.
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Unlike the complex glycans decorating the cell surface, the O-linked β-N-acetyl glucosamine (O-GlcNAc) modification is a simple intracellular Ser/Thr-linked monosaccharide that is important for disease-relevant signaling and enzyme regulation. O-GlcNAcylation requires uridine diphosphate–GlcNAc, a precursor responsive to nutrient status and other environmental cues. Alternative splicing of the genes encoding the O-GlcNAc cycling enzymes O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) yields isoforms targeted to discrete sites in the nucleus, cytoplasm, and mitochondria. OGT and OGA also partner with cellular effectors and act in tandem with other posttranslational modifications. The enzymes of O-GlcNAc cycling act preferentially on intrinsically disordered domains of target proteins impacting transcription, metabolism, apoptosis, organelle biogenesis, and transport.
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Pauli, Cornelius, Michael Kienhöfer, Stefanie Göllner und Carsten Müller-Tidow. „Epitranscriptomic modifications in acute myeloid leukemia: m6A and 2′-O-methylation as targets for novel therapeutic strategies“. Biological Chemistry 402, Nr. 12 (11.10.2021): 1531–46. http://dx.doi.org/10.1515/hsz-2021-0286.
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Abstract Modifications of RNA commonly occur in all species. Multiple enzymes are involved as writers, erasers and readers of these modifications. Many RNA modifications or the respective enzymes are associated with human disease and especially cancer. Currently, the mechanisms how RNA modifications impact on a large number of intracellular processes are emerging and knowledge about the pathogenetic role of RNA modifications increases. In Acute Myeloid Leukemia (AML), the N 6-methyladenosine (m6A) modification has emerged as an important modulator of leukemogenesis. The writer proteins METTL3 and METTL14 are both involved in AML pathogenesis and might be suitable therapeutic targets. Recently, close links between 2′-O-methylation (2′-O-me) of ribosomal RNA and leukemogenesis were discovered. The AML1-ETO oncofusion protein which specifically occurs in a subset of AML was found to depend on induction of snoRNAs and 2′-O-me for leukemogenesis. Also, NPM1, an important tumor suppressor in AML, was associated with altered snoRNAs and 2′-O-me. These findings point toward novel pathogenetic mechanisms and potential therapeutic interventions. The current knowledge and the implications are the topic of this review.
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Xiang, Meiyi, Wensu Liu, Wei Tian, Abin You und Dajun Deng. „RNA N-6-methyladenosine enzymes and resistance of cancer cells to chemotherapy and radiotherapy“. Epigenomics 12, Nr. 9 (Mai 2020): 801–9. http://dx.doi.org/10.2217/epi-2019-0358.
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Aim: As one of the early adaptive mechanisms by which cells respond to environmental changes, RNA modification appears to be a very promising target for cancer treatment. Results: RNA modifications are currently a hot topic in epigenetic research. Emerging experimental studies show that expression alterations of multiple m6A enzymes, including demethylase FTO, methyltransferase METTL3 and WTAP, mediate the development of resistance of cancer cells to various treatments. A set of small molecular chemical drugs targeted to these m6A enzymes are under development. Intervention of RNA m6A methylation is a possible therapeutic strategy to overcome drug resistance. Conclusions: RNA m6A methylation may play a crucial role in drug resistance development and intervention in cancer cells.
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van den Homberg, Daphne A. L., Reginald V. C. T. van der Kwast, Paul H. A. Quax und A. Yaël Nossent. „N-6-Methyladenosine in Vasoactive microRNAs during Hypoxia; A Novel Role for METTL4“. International Journal of Molecular Sciences 23, Nr. 3 (19.01.2022): 1057. http://dx.doi.org/10.3390/ijms23031057.
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N-6-methyladenosine (m6A) is the most prevalent post-transcriptional RNA modification in eukaryotic cells. The modification is reversible and can be dynamically regulated by writer and eraser enzymes. Alteration in the levels of these enzymes can lead to changes in mRNA stability, alternative splicing or microRNA processing, depending on the m6A-binding proteins. Dynamic regulation of mRNA m6A methylation after ischemia and hypoxia influences mRNA stability, alternative splicing and translation, contributing to heart failure. In this study, we studied vasoactive microRNA m6A methylation in fibroblasts and examined the effect of hypoxia on microRNAs methylation using m6A immunoprecipitation. Of the 19 microRNAs investigated, at least 16 contained m6A in both primary human fibroblasts and a human fibroblast cell line, suggesting vasoactive microRNAs are commonly m6A methylated in fibroblasts. More importantly, we found that mature microRNA m6A levels increased upon subjecting cells to hypoxia. By silencing different m6A writer and eraser enzymes followed by m6A immunoprecipitation, we identified METTL4, an snRNA m6A methyltransferase, to be predominantly responsible for the increase in m6A modification. Moreover, by using m6A-methylated microRNA mimics, we found that microRNA m6A directly affects downstream target mRNA repression efficacy. Our findings highlight the regulatory potential of the emerging field of microRNA modifications.
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Roll-Mecak, Antonina, Agnieszka Szyk und Vasilisa Kormendi. „Microtubule chemical complexity: mechanism of tubulin modification enzymes“. Acta Crystallographica Section A Foundations and Advances 70, a1 (05.08.2014): C1286. http://dx.doi.org/10.1107/s2053273314087130.
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Tubulin is subject to an abundant and diverse set of post-translational modifications that include phosphorylation, acetylation, poly-glutamylation, poly-glycylation and tyrosination. The highest density and variety of post-translational modifications are found in especially complex microtubule arrays like those of neurons or cilia. Not surprisingly, tubulin modification enzymes have been linked to human diseases including cancers and neurodegenerative disorders. I will present recent data from my lab on the mechanism of action of two tubulin modification enzymes that illustrate two divergent paradigms of tubulin recognition. Tubulin tyrosine ligase (TTL) adds a C-terminal Tyr to the exposed C-terminus of alpha-tubulin as part of a tyrosination/detyrosination cycle present in most eukaryotic cells. We solved the first crystal structure of tubulin tyrosine ligase that revealed how the TTL scaffold supported the expansion of the repertory of tubulin post-translational modification enzymes of the TTL like family that recognize either alpha- or beta-tubulin C-terminal tails. In addition to modifying tubulin, TTL also prevents tubulin from incorporating into microtubules by recognizing a tubulin dimer interface that would otherwise be involved in microtubule lattice interactions. I will also present recent work from my group on the structure and mechanism of action of tubulin acetyltransferase (TAT). TAT acetylates Lys-40 on alpha-tubulin in the microtubule lumen. We solved the 2.7Å structure of TAT bound to its ac-coA substrate as well as the 2.45Å structure of a catalytic inactive TAT mutant that reveals a domain swapped dimer in which the functionally essential N-terminus shows evidence of unprecedented structural plasticity. Implications for catalysis and microtubule stimulation of TAT activity will be discussed.
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Souza, G. M., D. P. Mehta, M. Lammertz, J. Rodriguez-Paris, R. Wu, J. A. Cardelli und H. H. Freeze. „Dictyostelium lysosomal proteins with different sugar modifications sort to functionally distinct compartments“. Journal of Cell Science 110, Nr. 18 (15.09.1997): 2239–48. http://dx.doi.org/10.1242/jcs.110.18.2239.
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Many Dictyostelium lysosomal enzymes contain mannose-6-phosphate (Man-6-P) in their N-linked oligosaccharide chains. We have now characterized a new group of lysosomal proteins that contain N-acetylglucosamine-1-phosphate (GlcNAc-1-P) linked to serine residues. GlcNAc-1-P-containing proteins, which include papain-like cysteine proteinases, cofractionate with the lysosomal markers and are in functional vesicles of the endosomal/lysosomal pathway. Immunoblots probed with reagents specific for each carbohydrate modification indicate that the lysosomal proteins are modified either by Man-6-P or GlcNAc-1-P, but not by both. Confocal microscopy shows that the two sets of proteins reside in physically and functionally distinct compartments. Vesicles with GlcNAc-1-P fuse with nascent bacteria-loaded phagosomes less than 3 minutes after ingestion, while those with Man-6-P do not participate in bacterial digestion until about 15 minutes after phagocytosis. Even though both types of vesicles fuse with phagosomes, GlcNAc-1-P- and Man-6-P-bearing proteins rarely colocalize. Since both lysosomal enzymes and their bound carbohydrate modifications are stable in lysosomes, a targeting or retrieval mechanism based on these carbohydrate modifications probably establishes and/or maintains segregation.
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Shima, Hiroki, und Kazuhiko Igarashi. „N 1-methyladenosine (m1A) RNA modification: the key to ribosome control“. Journal of Biochemistry 167, Nr. 6 (04.03.2020): 535–39. http://dx.doi.org/10.1093/jb/mvaa026.
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Abstract RNA displays diverse functions in living cells. The presence of various chemical modifications of RNA mediated by enzymes is one of the factors that impart such functional diversity to RNA. Among more than 100 types of RNA modification, N1-methyladenosine (m1A) is found mainly in tRNA and rRNA of many living organisms and is known to be deeply implicated in the topology or function of the two classes of RNA. In this commentary article, we would like to deal with the functional significance of m1A in RNA, and also to describe one methyltransferase installing m1A in a large subunit rRNA, whose orthologue in Caenorhabditis elegans was discovered recently and was reported in this journal.
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Kuldell, James C., Harshani Luknauth, Anthony E. Ricigliano und Nathan W. Rigel. „Biogenesis of Lipoproteins in Gram-Negative Bacteria: 50 Years of Progress“. Fine Focus 7, Nr. 1 (03.12.2021): 9–24. http://dx.doi.org/10.33043/ff.7.1.9-24.
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The outer membrane is the defining characteristic of Gram-negative bacteria and is crucial for the maintenance of cellular integrity. Lipoproteins are an essential component of this outer membrane and regulate broad cellular functions ranging from efflux, cellular physiology, antibiotic resistance, and pathogenicity. In the canonical model of lipoprotein biogenesis, lipoprotein precursors are first synthesized in the cytoplasm prior to extensive modifications by the consecutive action of three key enzymes: diacylglyceryl transferase (Lgt), lipoprotein signal peptidase A (LspA), and apolipoprotein N-acyltransferase (Lnt). This enzymatic process modifies lipoprotein precursors for subsequent trafficking by the Lol pathway. The function of these three enzymes were originally thought to be essential, however, in some Gram-negative bacteria, namely Acinetobacter baylyi, the third enzyme Lnt is dispensable. Here we review the function and significance of Lgt, LspA, and Lnt in outer membrane biogenesis and how non-canonical models of lipoprotein processing in Acinetobacter spp. can enhance our understanding of lipoprotein modifications and trafficking.
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Lorenz, Sonja. „Structural mechanisms of HECT-type ubiquitin ligases“. Biological Chemistry 399, Nr. 2 (26.01.2018): 127–45. http://dx.doi.org/10.1515/hsz-2017-0184.
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AbstractUbiquitin ligases (E3 enzymes) transfer ubiquitin from ubiquitin-conjugating (E2) enzymes to target proteins. By determining the selection of target proteins, modification sites on those target proteins, and the types of ubiquitin modifications that are formed, E3 enzymes are key specificity factors in ubiquitin signaling. Here, I summarize our knowledge of the structural mechanisms in the HECT E3 subfamily, many members of which play important roles in human disease. I discuss interactions of the conserved HECT domain with E2 enzymes, ubiquitin and target proteins, as well as macromolecular interactions with regulatory functions. While we understand individual steps in the catalytic cycle of HECT E3 enzymes on a structural level, this review also highlights key aspects that have yet to be elucidated. For instance, it remains unclear how diverse target proteins are presented to the catalytic center and how certain HECT E3 enzymes achieve specificity in ubiquitin linkage formation. The structural and functional properties of the N-terminal regions of HECT E3 enzymes that likely act as signaling hubs are also largely unknown. Structural insights into these aspects may open up routes for a therapeutic intervention with specific HECT E3 functions in distinct pathophysiological settings.
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Oh, Jang-Hyun, Ju-Yeon Hyun, Shun-Jia Chen und Alexander Varshavsky. „Five enzymes of the Arg/N-degron pathway form a targeting complex: The concept of superchanneling“. Proceedings of the National Academy of Sciences 117, Nr. 20 (04.05.2020): 10778–88. http://dx.doi.org/10.1073/pnas.2003043117.
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The Arg/N-degron pathway targets proteins for degradation by recognizing their N-terminal (Nt) residues. If a substrate bears, for example, Nt-Asn, its targeting involves deamidation of Nt-Asn, arginylation of resulting Nt-Asp, binding of resulting (conjugated) Nt-Arg to the UBR1-RAD6 E3-E2 ubiquitin ligase, ligase-mediated synthesis of a substrate-linked polyubiquitin chain, its capture by the proteasome, and substrate’s degradation. We discovered that the human Nt-Asn–specific Nt-amidase NTAN1, Nt-Gln–specific Nt-amidase NTAQ1, arginyltransferase ATE1, and the ubiquitin ligase UBR1-UBE2A/B (or UBR2-UBE2A/B) form a complex in which NTAN1 Nt-amidase binds to NTAQ1, ATE1, and UBR1/UBR2. In addition, NTAQ1 Nt-amidase and ATE1 arginyltransferase also bind to UBR1/UBR2. In the yeast Saccharomyces cerevisiae, the Nt-amidase, arginyltransferase, and the double-E3 ubiquitin ligase UBR1-RAD6/UFD4-UBC4/5 are shown to form an analogous targeting complex. These complexes may enable substrate channeling, in which a substrate bearing, for example, Nt-Asn, would be captured by a complex-bound Nt-amidase, followed by sequential Nt modifications of the substrate and its polyubiquitylation at an internal Lys residue without substrate’s dissociation into the bulk solution. At least in yeast, the UBR1/UFD4 ubiquitin ligase interacts with the 26S proteasome, suggesting an even larger Arg/N-degron–targeting complex that contains the proteasome as well. In addition, specific features of protein-sized Arg/N-degron substrates, including their partly sequential and partly nonsequential enzymatic modifications, led us to a verifiable concept termed “superchanneling.” In superchanneling, the synthesis of a substrate-linked poly-Ub chain can occur not only after a substrate’s sequential Nt modifications, but also before them, through a skipping of either some or all of these modifications within a targeting complex.
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Millar, A. Harvey, Joshua L. Heazlewood, Carmela Giglione, Michael J. Holdsworth, Andreas Bachmair und Waltraud X. Schulze. „The Scope, Functions, and Dynamics of Posttranslational Protein Modifications“. Annual Review of Plant Biology 70, Nr. 1 (29.04.2019): 119–51. http://dx.doi.org/10.1146/annurev-arplant-050718-100211.
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Assessing posttranslational modification (PTM) patterns within protein molecules and reading their functional implications present grand challenges for plant biology. We combine four perspectives on PTMs and their roles by considering five classes of PTMs as examples of the broader context of PTMs. These include modifications of the N terminus, glycosylation, phosphorylation, oxidation, and N-terminal and protein modifiers linked to protein degradation. We consider the spatial distribution of PTMs, the subcellular distribution of modifying enzymes, and their targets throughout the cell, and we outline the complexity of compartmentation in understanding of PTM function. We also consider PTMs temporally in the context of the lifetime of a protein molecule and the need for different PTMs for assembly, localization, function, and degradation. Finally, we consider the combined action of PTMs on the same proteins, their interactions, and the challenge ahead of integrating PTMs into an understanding of protein function in plants.
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Schaumburg, Anke, Hansjörg A. W. Schneider-Poetsch und C. Eckerskorn. „Characterization of Plastid 5-Aminolevulinate Dehydratase (ALAD; EC 4.2.1.24) from Spinach (Spinacia olevacea L.) by Sequencing and Comparison with Non-Plant ALAD Enzymes“. Zeitschrift für Naturforschung C 47, Nr. 1-2 (01.02.1992): 77–84. http://dx.doi.org/10.1515/znc-1992-1-214.
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Abstract We have sequenced 5-aminolevulinate dehydratase (ALAD; EC 2.4.1.24) of a plant. A fulllength cDNA clone (1727 bp) encoding this enzyme has been identified by immunoscreening a lambda gt 11 cDNA library of spinach. ALAD is not a plant-specific enzyme; however, the plant enzyme differs from the well known ALAD enzymes of bacteria, yeast and animals in structural and biochemical properties and in that it is located in the plastid. Differences and homologies can be traced back to the molecular level. The mature ALAD subunit, whose N-terminus was determined by automatic Edman degradation, is a protein of 367 amino acid residues and has a Mr of 40,132. This figure is in the range of molecular weights of non-plant ALADs. The active centre is highly conserved and the same is true for the ion-binding domain, except that 4 cysteines of the non-plant enzymes (binding Zn2+) have disappeared and a total of 6 aspartic acids meets the demands of Mg2+-binding. However, there are more distinct differences. Apart from a transit sequence of 56 amino acids targeting the plastid, the N-terminal part of the mature plant enzyme differs considerably from non-plant ALAD enzymes. It is rich in prolines and hydroxylated amino acids. The apparent Mr on SDS-PAGE is 45,000 or higher, but up to now posttranslational modifications have not been found.
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Portero-Otin, M., M. J. Bellmunt, J. R. Requena und R. Pamplona. „Protein modification by advanced Maillard adducts can be modulated by dietary polyunsaturated fatty acids“. Biochemical Society Transactions 31, Nr. 6 (01.12.2003): 1403–5. http://dx.doi.org/10.1042/bst0311403.
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Advanced Maillard adducts, such as N∊-(carboxymethyl)lysine and N∊-(carboxyethyl)lysine, can be formed efficiently in vitro from both peroxidation of polyunsaturated fatty acids and glycolysis intermediates. In an attempt to differentiate the in vivo influence of the two pathways in these modifications, Wistar rats were chronically fed with specially designed diets rich in saturated or unsaturated fats. The degree of fatty acid unsaturation of all analysed organs (liver, kidney, brain) was altered by these dietary stresses. Protein glycoxidative and lipoxidative modifications were measured by GC/MS. In accordance with fatty acid profiles, concentrations of N∊-(malondialdehyde)lysine in these tissues were significantly increased in animals fed the unsaturated fat diet. In contrast, N∊-(carboxymethyl)lysine and N∊-(carboxyethyl)lysine concentrations were strongly dependent on the tissue analysed; although the unsaturated fat diet increased their levels significantly in brain, levels were unchanged in kidney and decreased in liver. These later results could be interpreted on the basis that polyunsaturated fatty acids decrease the expression of several glycolytic enzymes in liver. Globally, these data suggest that tissue-specific metabolic characteristics play a key role in the degree of cellular protein modification by Maillard reactions, e.g. by modulation of the concentration of glycolysis intermediates or via specific defensive systems in these organs.
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Mishra, Suresh, Geetika Bassi und BL Grégoire Nyomba. „Inter-proteomic posttranslational modifications of the SARS-CoV-2 and the host proteins ‒ A new frontier“. Experimental Biology and Medicine 246, Nr. 7 (19.01.2021): 749–57. http://dx.doi.org/10.1177/1535370220986785.
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Posttranslational modification of proteins, which include both the enzymatic alterations of protein side chains and main-chain peptide bond connectivity, is a fundamental regulatory process that is crucial for almost every aspects of cell biology, including the virus-host cell interaction and the SARS-CoV-2 infection. The posttranslational modification of proteins has primarily been studied in cells and tissues in an intra-proteomic context (where both substrates and enzymes are part of the same species). However, the inter-proteomic posttranslational modifications of most of the SARS-CoV-2 proteins by the host enzymes and vice versa are largely unexplored in virus pathogenesis and in the host immune response. It is now known that the structural spike (S) protein of the SARS-CoV-2 undergoes proteolytic priming by the host serine proteases for entry into the host cells, and N- and O-glycosylation by the host cell enzymes during virion packaging, which enable the virus to spread. New evidence suggests that both SARS-CoV-2 and the host proteins undergo inter-proteomic posttranslational modifications, which play roles in virus pathogenesis and infection-induced immune response by hijacking the host cell signaling. The purpose of this minireview is to bring attention of the scientific community to recent cutting-edge discoveries in this understudied area. It is likely that a better insight into the molecular mechanisms involved may open new research directions, and thereby contribute to novel therapeutic modality development against the SARS-CoV-2. Here we briefly discuss the rationale and touch upon some unanswered questions in this context, especially those that require attention from the scientific community.
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Glassey, Emerson, Andrew M. King, Daniel A. Anderson, Zhengan Zhang und Christopher A. Voigt. „Functional expression of diverse post-translational peptide-modifying enzymes in Escherichia coli under uniform expression and purification conditions“. PLOS ONE 17, Nr. 9 (19.09.2022): e0266488. http://dx.doi.org/10.1371/journal.pone.0266488.
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RiPPs (ribosomally-synthesized and post-translationally modified peptides) are a class of pharmaceutically-relevant natural products expressed as precursor peptides before being enzymatically processed into their final functional forms. Bioinformatic methods have illuminated hundreds of thousands of RiPP enzymes in sequence databases and the number of characterized chemical modifications is growing rapidly; however, it remains difficult to functionally express them in a heterologous host. One challenge is peptide stability, which we addressed by designing a RiPP stabilization tag (RST) based on a small ubiquitin-like modifier (SUMO) domain that can be fused to the N- or C-terminus of the precursor peptide and proteolytically removed after modification. This is demonstrated to stabilize expression of eight RiPPs representative of diverse phyla. Further, using Escherichia coli for heterologous expression, we identify a common set of media and growth conditions where 24 modifying enzymes, representative of diverse chemistries, are functional. The high success rate and broad applicability of this system facilitates: (i) RiPP discovery through high-throughput “mining” and (ii) artificial combination of enzymes from different pathways to create a desired peptide.
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Steinbrecher, Tina, und Gerhard Leubner-Metzger. „Xyloglucan remodelling enzymes and the mechanics of plant seed and fruit biology“. Journal of Experimental Botany 73, Nr. 5 (02.03.2022): 1253–57. http://dx.doi.org/10.1093/jxb/erac020.
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This article comments on: Di Marzo M, Ebeling Viana V, Banfi C, Cassina V, Corti R, Herrera-Ubaldo H, Babolin N, Guazzotti A, Kiegle E, Gregis V, de Folter S, Sampedro J, Mantegazza F, Colombo L, Ezquer I. 2022. Cell wall modifications by α-XYLOSIDASE1 are required for the control of seed and fruit size. Journal of Experimental Botany 73, 1499–1515.
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Varland, Sylvia, Camilla Osberg und Thomas Arnesen. „N‐terminal modifications of cellular proteins: The enzymes involved, their substrate specificities and biological effects“. PROTEOMICS 15, Nr. 14 (16.06.2015): 2385–401. http://dx.doi.org/10.1002/pmic.201400619.
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Keffer-Wilkes, Laura Carole, Govardhan Reddy Veerareddygari und Ute Kothe. „RNA modification enzyme TruB is a tRNA chaperone“. Proceedings of the National Academy of Sciences 113, Nr. 50 (14.11.2016): 14306–11. http://dx.doi.org/10.1073/pnas.1607512113.
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Cellular RNAs are chemically modified by many RNA modification enzymes; however, often the functions of modifications remain unclear, such as for pseudouridine formation in the tRNA TΨC arm by the bacterial tRNA pseudouridine synthase TruB. Here we test the hypothesis that RNA modification enzymes also act as RNA chaperones. Using TruB as a model, we demonstrate that TruB folds tRNA independent of its catalytic activity, thus increasing the fraction of tRNA that can be aminoacylated. By rapid kinetic stopped-flow analysis, we identified the molecular mechanism of TruB’s RNA chaperone activity: TruB binds and unfolds both misfolded and folded tRNAs thereby providing misfolded tRNAs a second chance at folding. Previously, it has been shown that a catalytically inactive TruB variant has no phenotype when expressed in an Escherichia coli truB KO strain [Gutgsell N, et al. (2000) RNA 6(12):1870–1881]. However, here we uncover that E. coli strains expressing a TruB variant impaired in tRNA binding and in in vitro tRNA folding cannot compete with WT E. coli. Consequently, the tRNA chaperone activity of TruB is critical for bacterial fitness. In conclusion, we prove the tRNA chaperone activity of the pseudouridine synthase TruB, reveal its molecular mechanism, and demonstrate its importance for cellular fitness. We discuss the likelihood that other RNA modification enzymes are also RNA chaperones.
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Chung, Ben C., Jinshi Zhao, Robert A. Gillespie, Do-Yeon Kwon, Ziqiang Guan, Jiyong Hong, Pei Zhou und Seok-Yong Lee. „Crystal Structure of MraY, an Essential Membrane Enzyme for Bacterial Cell Wall Synthesis“. Science 341, Nr. 6149 (29.08.2013): 1012–16. http://dx.doi.org/10.1126/science.1236501.
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MraY (phospho-MurNAc-pentapeptide translocase) is an integral membrane enzyme that catalyzes an essential step of bacterial cell wall biosynthesis: the transfer of the peptidoglycan precursor phospho-MurNAc-pentapeptide to the lipid carrier undecaprenyl phosphate. MraY has long been considered a promising target for the development of antibiotics, but the lack of a structure has hindered mechanistic understanding of this critical enzyme and the enzyme superfamily in general. The superfamily includes enzymes involved in bacterial lipopolysaccharide/teichoic acid formation and eukaryotic N-linked glycosylation, modifications that are central in many biological processes. We present the crystal structure of MraY from Aquifex aeolicus (MraYAA) at 3.3 Å resolution, which allows us to visualize the overall architecture, locate Mg2+ within the active site, and provide a structural basis of catalysis for this class of enzyme.
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Fernández-Hernando, Carlos, Masaki Fukata, Pascal N. Bernatchez, Yuko Fukata, Michelle I. Lin, David S. Bredt und William C. Sessa. „Identification of Golgi-localized acyl transferases that palmitoylate and regulate endothelial nitric oxide synthase“. Journal of Cell Biology 174, Nr. 3 (24.07.2006): 369–77. http://dx.doi.org/10.1083/jcb.200601051.
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Lipid modifications mediate the subcellular localization and biological activity of many proteins, including endothelial nitric oxide synthase (eNOS). This enzyme resides on the cytoplasmic aspect of the Golgi apparatus and in caveolae and is dually acylated by both N-myristoylation and S-palmitoylation. Palmitoylation-deficient mutants of eNOS release less nitric oxide (NO). We identify enzymes that palmitoylate eNOS in vivo. Transfection of human embryonic kidney 293 cells with the complementary DNA (cDNA) for eNOS and 23 cDNA clones encoding the Asp-His-His-Cys motif (DHHC) palmitoyl transferase family members showed that five clones (2, 3, 7, 8, and 21) enhanced incorporation of [3H]-palmitate into eNOS. Human endothelial cells express all five of these enzymes, which colocalize with eNOS in the Golgi and plasma membrane and interact with eNOS. Importantly, inhibition of DHHC-21 palmitoyl transferase, but not DHHC-3, in human endothelial cells reduces eNOS palmitoylation, eNOS targeting, and stimulated NO production. Collectively, our data describe five new Golgi-targeted DHHC enzymes in human endothelial cells and suggest a regulatory role of DHHC-21 in governing eNOS localization and function.
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Galati, Rossella, Alessandra Verdina, Giuliana Falasca und Alberto Chersi. „Increased Resistance of Peptides to Serum Proteases by Modification of their Amino Groups“. Zeitschrift für Naturforschung C 58, Nr. 7-8 (01.08.2003): 558–61. http://dx.doi.org/10.1515/znc-2003-7-819.
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Abstract The ability of synthetic protein fragments to survive the degradative action of aminopeptidases and serum proteolytic enzymes can be remarkably enhanced by slight modifications at their N-terminal alpha-amino group. This can be achieved by addition of beta-alanine or amino acids of the d-configuration, amino acids which are seldom found in a living organism. These modifications do scarcely modify the chemical and physical properties of the peptides, and should be preferrred, especially for in vivo tests, to drastic alterations of peptides as produced by dinitrophenylation or dansylation of the amino groups.
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Yamauchi, Mitsuo, und Marnisa Sricholpech. „Lysine post-translational modifications of collagen“. Essays in Biochemistry 52 (25.05.2012): 113–33. http://dx.doi.org/10.1042/bse0520113.
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Type I collagen is the most abundant structural protein in vertebrates. It is a heterotrimeric molecule composed of two α1 chains and one α2 chain, forming a long uninterrupted triple helical structure with short non-triple helical telopeptides at both the N- and C-termini. During biosynthesis, collagen acquires a number of post-translational modifications, including lysine modifications, that are critical to the structure and biological functions of this protein. Lysine modifications of collagen are highly complicated sequential processes catalysed by several groups of enzymes leading to the final step of biosynthesis, covalent intermolecular cross-linking. In the cell, specific lysine residues are hydroxylated to form hydroxylysine. Then specific hydroxylysine residues located in the helical domain of the molecule are glycosylated by the addition of galactose or glucose-galactose. Outside the cell, lysine and hydroxylysine residues in the N- and C-telopeptides can be oxidatively deaminated to produce reactive aldehydes that undergo a series of non-enzymatic condensation reactions to form covalent intra- and inter-molecular cross-links. Owing to the recent advances in molecular and cellular biology, and analytical technologies, the biological significance and molecular mechanisms of these modifications have been gradually elucidated. This chapter provides an overview on these enzymatic lysine modifications and subsequent cross-linking.
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Ize, Bérengère, Sarah J. Coulthurst, Kostas Hatzixanthis, Isabelle Caldelari, Grant Buchanan, Elaine C. Barclay, David J. Richardson, Tracy Palmer und Frank Sargent. „Remnant signal peptides on non-exported enzymes: implications for the evolution of prokaryotic respiratory chains“. Microbiology 155, Nr. 12 (01.12.2009): 3992–4004. http://dx.doi.org/10.1099/mic.0.033647-0.
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The twin-arginine translocation (Tat) pathway is a prokaryotic protein targeting system dedicated to the transmembrane translocation of folded proteins. Substrate proteins are directed to the Tat translocase by signal peptides bearing a conserved SRRxFLK ‘twin-arginine’ motif. In Escherichia coli, most of the 27 periplasmically located Tat substrates are cofactor-containing respiratory enzymes, and many of these harbour a molybdenum cofactor at their active site. Molybdenum cofactor-containing proteins are not exclusively located in the periplasm, however, with the major respiratory nitrate reductase (NarG) and the biotin sulfoxide reductase (BisC), for example, being located at the cytoplasmic side of the membrane. Interestingly, both NarG and BisC contain ‘N-tail’ regions that bear some sequence similarity to twin-arginine signal peptides. In this work, we have examined the relationship between the non-exported N-tails and the Tat system. Using a sensitive genetic screen for Tat transport, variant N-tails were identified that displayed Tat transport activity. For the NarG 36-residue N-tail, six amino acid changes were needed to induce transport activity. However, these changes interfered with binding by the NarJ biosynthetic chaperone and impaired biosynthesis of the native enzyme. For the BisC 36-residue N-tail, only five amino acid substitutions were needed to restore Tat transport activity. These modifications also impaired in vivo BisC activity, but it was not possible to identify a biosynthetic chaperone for this enzyme. These data highlight an intimate genetic and evolutionary link between some non-exported redox enzymes and those transported across membranes by the Tat translocation system.
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Lubelski, Jacek, Wout Overkamp, Leon D. Kluskens, Gert N. Moll und Oscar P. Kuipers. „Influence of Shifting Positions of Ser, Thr, and Cys Residues in Prenisin on the Efficiency of Modification Reactions and on the Antimicrobial Activities of the Modified Prepeptides“. Applied and Environmental Microbiology 74, Nr. 15 (06.06.2008): 4680–85. http://dx.doi.org/10.1128/aem.00112-08.
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ABSTRACT Since the recent discovery that the nisin modification and transport machinery can be used to produce and modify peptides unrelated to nisin, specific questions arose concerning the specificity of the modification enzymes involved and the limits of their promiscuity with respect to the dehydration and cyclization processes. The nisin leader peptide has been postulated to fulfill a recognition and binding function required for these modifications. Here, we investigated whether the relative positions of the modifiable residues in the nisin prepeptide, with respect to the leader peptide, could influence the efficiency of their modification. We conducted a systematic study on the insertion of one to four alanines in front of either ring A or ring D to change the “reading frame” of modifiable residues, resulting in altered distance and topology of the modifiable residues relative to the leader. The insertion of N-terminal and hinge-located Ala residues had only a modest influence on the modification efficiency, demonstrating that the “phasing” of these residues relative to the leader peptide is not a critical factor in determining modification. However, in all cases, but especially with the N-terminal insertions, the antimicrobial activities of the fully modified nisin species were decreased.
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Chin, Hang Gyeong, Pierre-Olivier Esteve, Cristian Ruse, Jiyoung Lee, Scott E. Schaus, Sriharsa Pradhan und Ulla Hansen. „The microtubule-associated histone methyltransferase SET8, facilitated by transcription factor LSF, methylates α-tubulin“. Journal of Biological Chemistry 295, Nr. 14 (28.02.2020): 4748–59. http://dx.doi.org/10.1074/jbc.ra119.010951.
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Microtubules are cytoskeletal structures critical for mitosis, cell motility, and protein and organelle transport and are a validated target for anticancer drugs. However, how tubulins are regulated and recruited to support these distinct cellular processes is incompletely understood. Posttranslational modifications of tubulins are proposed to regulate microtubule function and dynamics. Although many of these modifications have been investigated, only one prior study reports tubulin methylation and an enzyme responsible for this methylation. Here we used in vitro radiolabeling, MS, and immunoblotting approaches to monitor protein methylation and immunoprecipitation, immunofluorescence, and pulldown approaches to measure protein–protein interactions. We demonstrate that N-lysine methyltransferase 5A (KMT5A or SET8/PR-Set7), which methylates lysine 20 in histone H4, bound α-tubulin and methylated it at a specific lysine residue, Lys311. Furthermore, late SV40 factor (LSF)/CP2, a known transcription factor, bound both α-tubulin and SET8 and enhanced SET8-mediated α-tubulin methylation in vitro. In addition, we found that the ability of LSF to facilitate this methylation is countered by factor quinolinone inhibitor 1 (FQI1), a specific small-molecule inhibitor of LSF. These findings suggest the general model that microtubule-associated proteins, including transcription factors, recruit or stimulate protein-modifying enzymes to target tubulins. Moreover, our results point to dual functions for SET8 and LSF not only in chromatin regulation but also in cytoskeletal modification.
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Mikolajczyk, Krzysztof, Radoslaw Kaczmarek und Marcin Czerwinski. „How glycosylation affects glycosylation: the role of N-glycans in glycosyltransferase activity“. Glycobiology 30, Nr. 12 (04.05.2020): 941–69. http://dx.doi.org/10.1093/glycob/cwaa041.
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Abstract N-glycosylation is one of the most important posttranslational modifications of proteins. It plays important roles in the biogenesis and functions of proteins by influencing their folding, intracellular localization, stability and solubility. N-glycans are synthesized by glycosyltransferases, a complex group of ubiquitous enzymes that occur in most kingdoms of life. A growing body of evidence shows that N-glycans may influence processing and functions of glycosyltransferases, including their secretion, stability and substrate/acceptor affinity. Changes in these properties may have a profound impact on glycosyltransferase activity. Indeed, some glycosyltransferases have to be glycosylated themselves for full activity. N-glycans and glycosyltransferases play roles in the pathogenesis of many diseases (including cancers), so studies on glycosyltransferases may contribute to the development of new therapy methods and novel glycoengineered enzymes with improved properties. In this review, we focus on the role of N-glycosylation in the activity of glycosyltransferases and attempt to summarize all available data about this phenomenon.
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Bakshi, Tania, David Pham, Raminderjeet Kaur und Bingyun Sun. „Hidden Relationships between N-Glycosylation and Disulfide Bonds in Individual Proteins“. International Journal of Molecular Sciences 23, Nr. 7 (29.03.2022): 3742. http://dx.doi.org/10.3390/ijms23073742.
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N-Glycosylation (NG) and disulfide bonds (DBs) are two prevalent co/post-translational modifications (PTMs) that are often conserved and coexist in membrane and secreted proteins involved in a large number of diseases. Both in the past and in recent times, the enzymes and chaperones regulating these PTMs have been constantly discovered to directly interact with each other or colocalize in the ER. However, beyond a few model proteins, how such cooperation affects N-glycan modification and disulfide bonding at selective sites in individual proteins is largely unknown. Here, we reviewed the literature to discover the current status in understanding the relationships between NG and DBs in individual proteins. Our results showed that more than 2700 human proteins carry both PTMs, and fewer than 2% of them have been investigated in the associations between NG and DBs. We summarized both these proteins with the reported relationships in the two PTMs and the tools used to discover the relationships. We hope that, by exposing this largely understudied field, more investigations can be encouraged to unveil the hidden relationships of NG and DBs in the majority of membranes and secreted proteins for pathophysiological understanding and biotherapeutic development.
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Mathur, Bhoomika, Asif Shajahan, Waqar Arif, Qiushi Chen, Nicholas J. Hand, Lara K. Abramowitz, Kristina Schoonjans et al. „Nuclear receptors FXR and SHP regulate protein N-glycan modifications in the liver“. Science Advances 7, Nr. 17 (April 2021): eabf4865. http://dx.doi.org/10.1126/sciadv.abf4865.
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Nuclear receptors farnesoid X receptor (FXR) and small heterodimer partner (SHP) are key regulators of metabolism. Here, we report a previously unknown function for the hepatic FXR-SHP axis in controlling protein N-linked glycosylation. Transcriptome analysis in liver-specific Fxr-Shp double knockout (LDKO) livers revealed induction of genes encoding enzymes in the N-glycosylation pathway, including Mgat5, Fut8, St3gal6, and St6gal1. FXR activation suppressed Mgat5, while Shp deletion induced St3gal6 and St6gal1. Increased percentages of core-fucosylated and triantennary glycan moieties were seen in LDKO livers, and proteins with the “hyperglycoforms” preferentially localized to exosomes and lysosomes. This up-regulation of N-glycosylation machinery was specific to the Golgi apparatus and not the endoplasmic reticulum. The increased glycan complexity in the LDKO correlated well with dilated unstacked Golgi ribbons and alterations in the secretion of albumin, cholesterol, and triglycerides. Our findings demonstrate a role for the FXR-SHP axis in maintaining glycoprotein diversity in the liver.
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Nair, Arathi, und Bhaskar Saha. „Regulation of Ras-GTPase Signaling and Localization by Post-Translational Modifications“. Kinases and Phosphatases 1, Nr. 2 (21.04.2023): 97–116. http://dx.doi.org/10.3390/kinasesphosphatases1020007.
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Ras, a GTP-GDP binary switch protein, transduces signals from diverse receptors to regulate various signaling networks. Three Ras genes encode for protein isoforms, namely, Harvey Ras (H-Ras), Kirsten Ras (K-Ras, with two splice variants, K-Ras4A and K-Ras4B), and Neuroblastoma Ras (N-Ras). The isoforms undergo a series of post-translational modifications that enable their membrane attachment and biological activity. The activation of Ras isoforms is tightly regulated, and any dysregulation affects cellular processes, such as cell division, apoptosis, differentiation, cell migration, etc. The Ras gene is highly prone to mutation, and ~30% of cancers carry somatic mutations in Ras, whereas germline mutations clinically manifest as various rasopathies. In addition to regulation by the Guanine nucleotide exchange factors and the GTPase activation proteins, Ras signaling, and localization are also regulated by phosphorylation-dephosphorylation, ubiquitination, nitrosylation, and acetylation. Herein, we review the regulation of Ras signaling and localization by various regulatory enzymes in depth and assess the current status of Ras drug discovery targeting these regulatory enzymes.
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Kolli, Nagamalleswari, Jowita Mikolajczyk, Marcin Drag, Debaditya Mukhopadhyay, Nela Moffatt, Mary Dasso, Guy Salvesen und Keith D. Wilkinson. „Distribution and paralogue specificity of mammalian deSUMOylating enzymes“. Biochemical Journal 430, Nr. 2 (13.08.2010): 335–44. http://dx.doi.org/10.1042/bj20100504.
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The covalent attachment of SUMO (small ubiquitin-like protein modifier) to target proteins results in modifications in their activity, binding interactions, localization or half-life. The reversal of this modification is catalysed by SENPs (SUMO-specific processing proteases). Mammals contain four SUMO paralogues and six SENP enzymes. In the present paper, we describe a systematic analysis of human SENPs, integrating estimates of relative selectivity for SUMO1 and SUMO2, and kinetic measurements of recombinant C-terminal cSENPs (SENP catalytic domains). We first characterized the reaction of each endogenous SENP and cSENPs with HA–SUMO-VS [HA (haemagglutinin)-tagged SUMO-vinyl sulfones], active-site-directed irreversible inhibitors of SENPs. We found that all cSENPs and endogenous SENP1 react with both SUMO paralogues, whereas all other endogeneous SENPs in mammalian cells and tissues display high selectivity for SUMO2-VS. To obtain more quantitative data, the kinetic properties of purified cSENPs were determined using SUMO1- or SUMO2-AMC (7-amino-4-methylcoumarin) as substrate. All enzymes bind their respective substrates with high affinity. cSENP1 and cSENP2 process either SUMO substrate with similar affinity and catalytic efficiency; cSENP5 and cSENP6 show marked catalytic specificity for SUMO2 as measured by Km and kcat, whereas cSENP7 works only on SUMO2. Compared with cSENPs, recombinant full-length SENP1 and SENP2 show differences in SUMO selectivity, indicating that paralogue specificity is influenced by the presence of the variable N-terminal domain of each SENP. Our data suggest that SUMO2 metabolism is more dynamic than that of SUMO1 since most SENPs display a marked preference for SUMO2.
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Larsen, Karen, Roberto Najle, Adrián Lifschitz, María L. Maté, Carlos Lanusse und Guillermo L. Virkel. „Effects of Sublethal Exposure to a Glyphosate-Based Herbicide Formulation on Metabolic Activities of Different Xenobiotic-Metabolizing Enzymes in Rats“. International Journal of Toxicology 33, Nr. 4 (Juli 2014): 307–18. http://dx.doi.org/10.1177/1091581814540481.
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The activities of different xenobiotic-metabolizing enzymes in liver subcellular fractions from Wistar rats exposed to a glyphosate (GLP)-based herbicide (Roundup full II) were evaluated in this work. Exposure to the herbicide triggered protective mechanisms against oxidative stress (increased glutathione peroxidase activity and total glutathione levels). Liver microsomes from both male and female rats exposed to the herbicide had lower (45%-54%, P < 0.01) hepatic cytochrome P450 (CYP) levels compared to their respective control animals. In female rats, the hepatic 7-ethoxycoumarin O-deethylase (a general CYP-dependent enzyme activity) was 57% higher ( P < 0.05) in herbicide-exposed compared to control animals. Conversely, this enzyme activity was 58% lower ( P < 0.05) in male rats receiving the herbicide. Lower ( P < 0.05) 7-ethoxyresorufin O-deethlyase (EROD, CYP1A1/2 dependent) and oleandomycin triacetate (TAO) N-demethylase (CYP3A dependent) enzyme activities were observed in liver microsomes from exposed male rats. Conversely, in females receiving the herbicide, EROD increased (123%-168%, P < 0.05), whereas TAO N-demethylase did not change. A higher (158%-179%, P < 0.01) benzyloxyresorufin O-debenzylase (a CYP2B-dependent enzyme activity) activity was only observed in herbicide-exposed female rats. In herbicide-exposed rats, the hepatic S-oxidation of methimazole (flavin monooxygenase dependent) was 49% to 62% lower ( P < 0.001), whereas the carbonyl reduction of menadione (a cytosolic carbonyl reductase-dependent activity) was higher ( P < 0.05). Exposure to the herbicide had no effects on enzymatic activities dependent on carboxylesterases, glutathione transferases, and uridinediphospho-glucuronosyltransferases. This research demonstrated certain biochemical modifications after exposure to a GLP-based herbicide. Such modifications may affect the metabolic fate of different endobiotic and xenobiotic substances. The pharmacotoxicological significance of these findings remains to be clarified.
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Høegh, Inge, Shamkant Patkar, Torben Halkier und Mogens T. Hansen. „Two lipases from Candida antarctica: cloning and expression in Aspergillus oryzae“. Canadian Journal of Botany 73, S1 (31.12.1995): 869–75. http://dx.doi.org/10.1139/b95-333.
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The basidiomycetous yeast Candida antarctica expresses two lipases that possess widely different properties. The genes LIPA and LIPB encoding both lipases were cloned and sequenced. Both lipases were secreted efficiently from Aspergillus oryzae transformed with lipase expression plasmids. N-Glycosylation was slightly more extensive in the heterologously expressed enzymes than in those purified from C. antarctica, but the enzymatic characteristics were retained. Both enzymes are encoded as preproenzymes. Proteolytic processing of the primary translation product was efficient in A. oryzae and resulted in the same N-terminals as in C. antarctica. Modifications or deletions of the propeptide of lipase component B did not prevent efficient secretion of active lipase from A. oryzae. Alternative proteolytic processing of the modified propeptides was detected. Key words: Lipase, Candida, cloning, Aspergillus, expression, propeptide.
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Perez-Rizquez, Carlos, David Lopez-Tejedor, Laura Plaza-Vinuesa, Blanca de las Rivas, Rosario Muñoz, Jose Cumella und Jose M. Palomo. „Chemical Modification of Novel Glycosidases from Lactobacillus plantarum Using Hyaluronic Acid: Effects on High Specificity against 6-Phosphate Glucopyranoside“. Coatings 9, Nr. 5 (09.05.2019): 311. http://dx.doi.org/10.3390/coatings9050311.
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Three novel glycosidases produced from Lactobacillus plantarum, so called Lp_0440, Lp_2777, and Lp_3525, were isolated and overexpressed on Escherichia coli containing a His-tag for specific purification. Their specific activity was evaluated against the hydrolysis of p-nitrophenylglycosides and p-nitrophenyl-6-phosphate glycosides (glucose and galactose) at pH 7. All three were modified with hyaluronic acid (HA) following two strategies: A simple coating by direct incubation at alkaline pH or direct chemical modification at pH 6.8 through preactivation of HA with carbodiimide (EDC) and N-hydroxysuccinimide (NHS) at pH 4.8. The modifications exhibited important effect on enzyme activity and specificity against different glycopyranosides in the three cases. Physical modification showed a radical decrease in specific activity on all glycosidases, without any significant change in enzyme specificity toward monosaccharide (glucose or galactose) or glycoside (C-6 position free or phosphorylated). However, the surface covalent modification of the enzymes showed very interesting results. The glycosidase Lp_0440 showed low glycoside specificity at 25 °C, showing the same activity against p-nitrophenyl-glucopyranoside (pNP-Glu) or p-nitrophenyl-6-phosphate glucopyranoside (pNP-6P-Glu). However, the conjugated cHA-Lp_0440 showed a clear increase in the specificity towards the pNP-Glu and no activity against pNP-6P-Glu. The other two glycosidases (Lp_2777 and Lp_3525) showed high specificity towards pNP-6P-glycosides, especially to the glucose derivative. The HA covalent modification of Lp_3525 (cHA-Lp_3525) generated an enzyme completely specific against the pNP-6P-Glu (phosphoglycosidase) maintaining more than 80% of the activity after chemical modification. When the temperature was increased, an alteration of selectivity was observed. Lp_0440 and cHA-Lp_0440 only showed activity against p-nitrophenyl-galactopyranoside (pNP-Gal) at 40 °C, higher than at 25 °C in the case of the conjugated enzyme.
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Mahapatra, Sebabrata, Tetsuya Yagi, John T. Belisle, Benjamin J. Espinosa, Preston J. Hill, Michael R. McNeil, Patrick J. Brennan und Dean C. Crick. „Mycobacterial Lipid II Is Composed of a Complex Mixture of Modified Muramyl and Peptide Moieties Linked to Decaprenyl Phosphate“. Journal of Bacteriology 187, Nr. 8 (15.04.2005): 2747–57. http://dx.doi.org/10.1128/jb.187.8.2747-2757.2005.
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ABSTRACT Structural analysis of compounds identified as lipid I and II from Mycobacterium smegmatis demonstrated that the lipid moiety is decaprenyl phosphate; thus, M. smegmatis is the first bacterium reported to utilize a prenyl phosphate other than undecaprenyl phosphate as the lipid carrier involved in peptidoglycan synthesis. In addition, mass spectrometry showed that the muropeptides from lipid I are predominantly N-acetylmuramyl-l-alanine-d-glutamate-meso-diaminopimelic acid-d-alanyl-d-alanine, whereas those isolated from lipid II form an unexpectedly complex mixture in which the muramyl residue and the pentapeptide are modified singly and in combination. The muramyl residue is present as N-acetylmuramic acid, N-glycolylmuramic acid, and muramic acid. The carboxylic functions of the peptide side-chains of lipid II showed three types of modification, with the dominant one being amidation. The preferred site for amidation is the free carboxyl group of the meso-diaminopimelic acid residue. Diamidated species were also observed. The carboxylic function of the terminal d-alanine of some molecules is methylated, as are all three carboxylic acid functions of other molecules. This study represents the first structural analysis of mycobacterial lipid I and II and the first report of extensive modifications of these molecules. The observation that lipid I was unmodified strongly suggests that the lipid II intermediates of M. smegmatis are substrates for a variety of enzymes that introduce modifications to the sugar and amino acid residues prior to the synthesis of peptidoglycan.
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McEllistrem, M. Catherine, Janet E. Stout und Lee H. Harrison. „Simplified Protocol for Pulsed-Field Gel Electrophoresis Analysis of Streptococcus pneumoniae“. Journal of Clinical Microbiology 38, Nr. 1 (Januar 2000): 351–53. http://dx.doi.org/10.1128/jcm.38.1.351-353.2000.
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ABSTRACT A variety of pulsed-field gel electrophoresis (PFGE) protocols for the molecular subtyping of Streptococcus pneumoniae have been reported; most are time-consuming and complex. We sought to modify reference PFGE protocols to reduce the time required while creating high-quality gels. Only protocol modifications that resulted in high-quality banding patterns were considered. The following protocol components were modified. Lysis enzymes (lysozyme, mutanolysin, and RNase A) were deleted in a stepwise fashion, and then the lysis buffer was deleted. Lysis and digestion were accomplished in a single step with EDTA and N -lauroyl sarcosine (ES; pH 8.5 to 9.3) incubation at 50°C in the absence of proteinase K. All enzymes except the restriction enzyme were omitted. A minimum incubation time of 6 h was required to achieve high-quality gels. All of the reactions were performed within 9 h, and the total protocol time from lysis to gel completion was reduced from 3 days to only 36 h. Combining lysis and digestion into a single step resulted in a substantial reduction in the time required to perform PFGE for S. pneumoniae . The ES solution may have caused cell lysis by activating N -acetylmuramyl- l -alanine amidase, the pneumococcal autolysin.
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Spooren, Anita AMG, und Chris TA Evelo. „Only the glutathione dependent antioxidant enzymes are inhibited by haematotoxic hydroxylamines“. Human & Experimental Toxicology 17, Nr. 10 (Oktober 1998): 554–59. http://dx.doi.org/10.1177/096032719801701005.
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Hydroxylamine and some of its derivatives are known to cause oxidative effects both in vitro and in vivo.Inthe current study we investigated the effects of hydroxyla-mines on the enzymatic antioxidant defense system in human erythrocytes. The activity of catalase and super-oxide dismutase was not significantly influenced by any of the hydroxylamines tested. However, the activity of glutathione peroxidase (GPX) and glutathione S-transferase (GST) was strongly inhibited by hydroxylamine and its O-derivatives (O-methyl and O-ethyl hydroxylamine). GPX was also inhibited by two N-derivatives of hydro-xylamine (i.e. N-dimethyl and N, O-dimethyl hydroxyla-mine). This indicates that exposure to hydroxylamines not only changes the cellular oxidation-reduction status but also leads to inhibition of the glutathione dependent antioxidant enzymes. GST as well as GPX have cysteine residues at the active site of the enzymes. Such an accessible thiol group is generally susceptible to formation of protein-mixed disulphides or intramolecular disulphides. If these thiol groups are essential for activity this would be accompanied by an increase or decrease in the enzyme activity. In principle this is also true for glutathione reductase (GR), which in this study was only inhibited by N, O-dimethyl and N-methyl hydroxylamines. However, GR is capable to reduce these disulphides by taking up two electrons, either from its substrate NAPDH or from another reductant. Oxidation of these thiol groups in GR would thus not lead to impairment of GR activity. The fact that NODMH and NMH do decrease the GR activity can therefore only be explained by other modifications. The activity loss of GST and GPX on the other hand, is likely to involve oxidation of critical cysteine residues. The practical consequence of these findings is that the cellular prooxidant state that may arise in erythrocytes exposed to hydroxylamines can be further increased by activity loss of protective enzymes, which may decrease the average life span of the red blood cell.
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Amjadi, Mohammad, Tooba Hallaj und Niko Hildebrandt. „A sensitive homogeneous enzyme assay for euchromatic histone-lysine-N-methyltransferase 2 (G9a) based on terbium-to-quantum dot time-resolved FRET“. BioImpacts 11, Nr. 3 (08.07.2020): 173–79. http://dx.doi.org/10.34172/bi.2021.23.
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Introduction: Histone modifying enzymes include several classes of enzymes that are responsible for various post-translational modifications of histones such as methylation and acetylation. They are important epigenetic factors, which may involve several diseases and so their assay, as well as screening of their inhibitors, are of great importance. Herein, a bioassay based on terbium-to-quantum dot (Tb-to-QD) time-resolved Förster resonance energy transfer (TR-FRET) was developed for monitoring the activity of G9a, the euchromatic histone-lysine N-methyltransferase 2. Overexpression of G9a has been reported in some cancers such as ovarian carcinoma, lung cancer, multiple myeloma and brain cancer. Thus, inhibition of this enzyme is important for therapeutic purposes. Methods: In this assay, a biotinylated peptide was used as a G9a substrate in conjugation with streptavidin-coated ZnS/CdSe QD as FRET acceptor, and an anti-mark antibody labeled with Tb as a donor. Time-resolved fluorescence was used for measuring FRET ratios. Results: We examined three QDs, with emission wavelengths of 605, 655 and 705 nm, as FRET acceptors and investigated FRET efficiency between the Tb complex and each of them. Since the maximum FRET efficiency was obtained for Tb to QD705 (more than 50%), this pair was exploited for designing the enzyme assay. We showed that the method has excellent sensitivity and selectivity for the determination of G9a at concentrations as low as 20 pM. Furthermore, the designed assay was applied for screening of an enzyme inhibitor, S-(5’-Adenosyl)-L-homocysteine (SAH). Conclusion: It was shown that Tb-to-QD FRET is an outstanding platform for developing a homogenous assay for the G9a enzyme and its inhibitors. The obtained results confirmed that this assay was quite sensitive and could be used in the field of inhibitor screening.
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Sim, E., K. Pinter, A. Mushtaq, A. Upton, J. Sandy, S. Bhakta und M. Noble. „Arylamine N-acetyltransferases: a pharmacogenomic approach to drug metabolism and endogenous function“. Biochemical Society Transactions 31, Nr. 3 (01.06.2003): 615–19. http://dx.doi.org/10.1042/bst0310615.
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The arylamine N-acetyltransferases (NATs) are a unique family of enzymes that catalyse the transfer of an acetyl group from acetyl-CoA to the terminal nitrogen of hydrazine and arylamine drugs and carcinogens. The NATs have been shown to be important in drug detoxification and carcinogen activation, with humans possessing two isoenzymes encoded by polymorphic genes. This polymorphism has pharmacogenetic implications, leading to different rates of inactivation of drugs, including the anti-tubercular agent isoniazid and the anti-hypertensive drug hydralazine. Mice provide a good model for human NAT, allowing genetic manipulation of expression to explore possible endogenous roles of these enzymes. The first three-dimensional NAT structure was resolved for NAT from Salmonella typhimurium, and subsequently the structure of NAT from Mycobacterium smegmatis has been elucidated. These identified a ‘Cys-His-Asp’ catalytic triad (conserved in all NATs), which is believed to be responsible for the activation of the active site cysteine residue. As more genomic data become available, NAT homologues continue to be found in prokaryotic species, many of which are pathogenic, including Mycobacterium tuberculosis. The discovery of NAT in M. tuberculosis is particularly significant, since this enzyme participates in inactivation of isoniazid in the bacterium, with implications for isoniazid resistance. Structural studies on NAT proteins and phenotypic analyses of organisms (both mice and prokaryotes) following genetic modifications of the nat genes are leading to an understanding of the potentially diverse roles of NAT in endogenous and xenobiotic metabolism. These studies have indicated that NAT, particularly in Mycobacteria, has the potential to be a drug target. Combinatorial chemical approaches, together with in silico structural studies, will allow for advances in the identification of NAT substrates and inhibitors, both as experimental tools and as potential drugs.
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Zheng, Suting, John J. Wyrick und Joseph C. Reese. „Novel trans-Tail Regulation of H2B Ubiquitylation and H3K4 Methylation by the N Terminus of Histone H2A“. Molecular and Cellular Biology 30, Nr. 14 (24.05.2010): 3635–45. http://dx.doi.org/10.1128/mcb.00324-10.
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ABSTRACT Chromatin is regulated by cross talk among different histone modifications, which can occur between residues within the same tail or different tails in the nucleosome. The latter is referred to as trans-tail regulation, and the best-characterized example of this is the dependence of H3 methylation on H2B ubiquitylation. Here we describe a novel form of trans-tail regulation of histone modifications involving the N-terminal tail of histone H2A. Mutating or deleting residues in the N-terminal tail of H2A reduces H2B ubiquitylation and H3K4 methylation but does not affect the recruitment of the modifying enzymes, Rad6/Bre1 and COMPASS, to genes. The H2A tail is required for the incorporation of Cps35 into COMPASS, and increasing the level of ubiquitylated H2B in H2A tail mutants suppresses the H3K4 methylation defect, suggesting that the H2A tail regulates H2B-H3 cross talk. We mapped the region primarily responsible for this regulation to the H 2 A r epression domain, HAR. The HAR and K123 of H2B are in close proximity to each other on the nucleosome, suggesting that they form a docking site for the ubiquitylation machinery. Interestingly, the HAR is partially occluded by nucleosomal DNA, suggesting that the function of the H2A cross talk pathway is to restrict histone modifications to nucleosomes altered by transcription.
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Næssan, Cecilia L., Wolfgang Egge-Jacobsen, Ryan W. Heiniger, Matthew C. Wolfgang, Finn Erik Aas, Åsmund Røhr, Hanne C. Winther-Larsen und Michael Koomey. „Genetic and Functional Analyses of PptA, a Phospho-Form Transferase Targeting Type IV Pili in Neisseria gonorrhoeae“. Journal of Bacteriology 190, Nr. 1 (19.10.2007): 387–400. http://dx.doi.org/10.1128/jb.00765-07.
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ABSTRACT The PilE pilin subunit protein of Neisseria gonorrhoeae undergoes unique covalent modifications with phosphoethanolamine (PE) and phosphocholine (PC). The pilin phospho-form transferase A (PptA) protein, required for these modifications, shows sequence relatedness with and architectural similarities to lipopolysaccharide PE transferases. Here, we used regulated expression and mutagenesis as means to better define the relationships between PptA structure and function, as well as to probe the mechanisms by which other factors impact the system. We show here that pptA expression is coupled at the level of transcription to its distal gene, murF, in a division/cell wall gene operon and that PptA can act in a dose-dependent fashion in PilE phospho-form modification. Molecular modeling and site-directed mutagenesis provided the first direct evidence that PptA is a member of the alkaline phosphatase superfamily of metalloenzymes with similar metal-binding sites and conserved structural folds. Through phylogenetic analyses and sequence alignments, these conclusions were extended to include the lipopolysaccharide PE transferases, including members of the disparate Lpt6 subfamily, and the MdoB family of phosphoglycerol transferases. Each of these enzymes thus likely acts as a phospholipid head group transferase whose catalytic mechanism involves a trans-esterification step generating a protein-phospho-form ester intermediate. Coexpression of PptA with PilE in Pseudomonas aeruginosa resulted in high levels of PE modification but was not sufficient for PC modification. This and other findings show that PptA-associated PC modification is governed by as-yet-undefined ancillary factors unique to N. gonorrhoeae.
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Patel, Chaitanya, Haddas Saad, Marina Shenkman und Gerardo Z. Lederkremer. „Oxidoreductases in Glycoprotein Glycosylation, Folding, and ERAD“. Cells 9, Nr. 9 (22.09.2020): 2138. http://dx.doi.org/10.3390/cells9092138.
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N-linked glycosylation and sugar chain processing, as well as disulfide bond formation, are among the most common post-translational protein modifications taking place in the endoplasmic reticulum (ER). They are essential modifications that are required for membrane and secretory proteins to achieve their correct folding and native structure. Several oxidoreductases responsible for disulfide bond formation, isomerization, and reduction have been shown to form stable, functional complexes with enzymes and chaperones that are involved in the initial addition of an N-glycan and in folding and quality control of the glycoproteins. Some of these oxidoreductases are selenoproteins. Recent studies also implicate glycan machinery–oxidoreductase complexes in the recognition and processing of misfolded glycoproteins and their reduction and targeting to ER-associated degradation. This review focuses on the intriguing cooperation between the glycoprotein-specific cell machineries and ER oxidoreductases, and highlights open questions regarding the functions of many members of this large family.
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Ran, Di, Yong-guo Zhang und Jun Sun. „IHIBITION OF TRNA QUEUOSINE MODIFICATION CAUSE MITOCHONDRIAL DYSFUNCTION AND APOPTOSIS IN THE INTESTINAL EPITHELIAL CELLS“. Inflammatory Bowel Diseases 30, Supplement_1 (25.01.2024): S67—S68. http://dx.doi.org/10.1093/ibd/izae020.145.
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Abstract BACKGROUND Transfer RNA (tRNA) modifications occur through the action of specific enzymes that recognize and modify the nucleotides within the tRNA molecule. Queuine tRNA-ribosyltransferase catalytic subunit 1 (QTRT1) and QTRT 2 co-localize in mitochondria and form a heterodimeric TGT participating in tRNA Queuosine (tRNA-Q) modification. Our previous study demonstrated that Q-tRNA modification plays a novel role in regulating barrier functions of intestinal epithelial cells. However, the roles of tRNA-Q modifications in the maintenance of intestinal mitochondrial homeostasis and the progression of inflammatory bowel disease (IBD) are still unclear. METHODS We used QTRT1 knockout (KO) mice and cultured cell lines with QTRT1 knockdown (KD) to investigate the impact and mechanism of tRNA-Q modifications in intestinal mitochondrial homeostasis and inflammation. RESULTS Initially, we confirmed QTRT1's mitochondrial localization through immunofluorescence co-localization with Mitotracker staining in QTRT1 KD CaCO2-BBE cells. Then we used flow cytometry MitoSox Red staining and revealed an increase in mitochondrial ROS production in QTRT1 KD cells. Furthermore, we observed heightened mitophagy both in vitro and in the colon of QTRT1KO mice, evident through significantly enhanced fusion of Mtphagy Dye-labeled mitochondria with lysosomes, and altered mitochondrial proteins (Tomm20, LC3, and Cytochrome C) via Western Blotting. Notably, we identified an increase in apoptosis in the QTRT1 KO mice evidenced by the upregulation of phosphorylated PARP, cleaved Caspase 3, and the Bax/BCL-2 ratio in colonic mitochondrial proteins. TUNEL staining corroborated this apoptosis increase specifically in the colon due to the QTRT1 deficiency. CONCLUSIONS Reduced QTRT1 induced dysfunctional mitochondria and Caspase-3 dependent apoptosis. tRNA-Q modification plays an unexplored role in the pathogenesis of mitochondrial function in the intestine. Our upcoming research will employ N-acetyl-l-cysteine, a mitochondrial ROS inhibitor, and a Caspase 3 specific inhibitor to ascertain the role of tRNA modification in mitochondrial function in the intestinal inflammation. Insights into tRNA-Q modification will pave the road for new therapeutic strategies to restore mitochondrial function in IBD.
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Avila, C., R. Huang, M. Stevens, A. Aponte, D. Tripodi, K. Kim und M. Sack. „Platelet Mitochondrial Dysfunction is Evident in Type 2 Diabetes in Association with Modifications of Mitochondrial Anti-Oxidant Stress Proteins“. Experimental and Clinical Endocrinology & Diabetes 120, Nr. 04 (15.09.2011): 248–51. http://dx.doi.org/10.1055/s-0031-1285833.
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AbstractMitochondrial dysfunction and oxidative stress in insulin responsive tissues is implicated in the pathogenesis of type 2 diabetes. Whether these perturbations extend to other tissues and contribute to their pathophysiology is less well established. The objective of this study was to investigate platelet mitochondria to evaluate whether type 2 diabetes associated mitochondrial dysfunction is evident in circulating cells.A pilot study of mitochondrial respiratory function and proteomic changes comparing platelets extracted from insulin sensitive (n=8) and type 2 diabetic subjects (n=7). In-situ platelet mitochondria show diminished oxygen consumption and lower oxygen-dependent ATP synthesis in diabetic vs. control subjects. Mass spectrometric identification and confirmatory immunoblot analysis identifies induction of the mitochondrial anti-oxidant enzymes superoxide dismutase 2 and thioredoxin-dependent peroxide reductase 3 in platelets of diabetic subjects. As oxidative stress upregulates anti-oxidant enzymes we assessed mitochondrial protein carbonylation as an index of oxidative-stress. Platelets of diabetic subjects exhibit significantly increased protein carbonylation compared to controls.As platelets are anuclear fragments of megakaryocytes, our data suggest that the bone marrow compartment in type 2 diabetic subjects is exposed to increased mitochondrial oxidative stress with upregulation of nuclear-encoded antioxidant mitochondrial enzymes. This ‘stress-signature’ in platelets of diabetic subjects is associated with a diminution of their mitochondrial contribution to energy production and support that mitochondrial perturbations in type 2 diabetes extends beyond the classical insulin responsive tissues. Platelets, as “accessible human tissue”, may be useful to measure the mitochondrial modulatory effects of emerging anti-diabetic therapeutics.
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Potter, Beth A., Rebecca P. Hughey und Ora A. Weisz. „Role of N- and O-glycans in polarized biosynthetic sorting“. American Journal of Physiology-Cell Physiology 290, Nr. 1 (Januar 2006): C1—C10. http://dx.doi.org/10.1152/ajpcell.00333.2005.
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The maintenance of proper epithelial function requires efficient sorting of newly synthesized and recycling proteins to the apical and basolateral surfaces of differentiated cells. Whereas basolateral protein sorting signals are generally confined to their cytoplasmic regions, apical targeting signals have been identified that localize to luminal, transmembrane, and cytoplasmic aspects of proteins. In the past few years, both N- and O-linked glycans have been identified as apical sorting determinants. Glycan structures are extraordinarily diverse and have tremendous information potential. Moreover, because the oligosaccharides added to a given protein can change depending on cell type and developmental stage, the potential exists for altering sorting pathways by modulation of the expression pattern of enzymes involved in glycan synthesis. In this review, we discuss the evidence for glycan-mediated apical sorting along the biosynthetic pathway and present possible mechanisms by which these common and heterogeneous posttranslational modifications might function as specific sorting signals.
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Lucas, Jose Antonio, Ana Garcia-Villaraco, Maria Belen Montero-Palmero, Blanca Montalban, Beatriz Ramos Solano und Francisco Javier Gutierrez-Mañero. „Physiological and Genetic Modifications Induced by Plant-Growth-Promoting Rhizobacteria (PGPR) in Tomato Plants under Moderate Water Stress“. Biology 12, Nr. 7 (23.06.2023): 901. http://dx.doi.org/10.3390/biology12070901.
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Physiological, metabolic, and genetic changes produced by two plant growth promoting rhizobacteria (PGPR) Pseudomonas sp. (internal code of the laboratory: N 5.12 and N 21.24) inoculated in tomato plants subjected to moderate water stress (10% polyethylene glycol-6000; PEG) were studied. Photosynthesis efficiency, photosynthetic pigments, compatible osmolytes, reactive oxygen species (ROS) scavenging enzymes activities, oxidative stress level and expression of genes related to abscisic acid synthesis (ABA; 9-cis-epoxycarotenoid dioxygenase NCDE1 gene), proline synthesis (Pyrroline-5-carboxylate synthase P5CS gene), and plasma membrane ATPase (PM ATPase gene) were measured. Photosynthetic efficiency was compromised by PEG, but bacterial-inoculated plants reversed the effects: while N5.12 increased carbon fixation (37.5%) maintaining transpiration, N21.24 increased both (14.2% and 31%), negatively affecting stomatal closure, despite the enhanced expression of NCDE1 and plasma membrane ATPase genes, evidencing the activation of different adaptive mechanisms. Among all parameters evaluated, photosynthetic pigments and antioxidant enzymes guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) responded differently to both strains. N 5.12 increased photosynthetic pigments (70% chlorophyll a, 69% chlorophyll b, and 65% carotenoids), proline (33%), glycine betaine (4.3%), and phenolic compounds (21.5%) to a greater extent, thereby decreasing oxidative stress (12.5% in Malondialdehyde, MDA). Both bacteria have highly beneficial effects on tomato plants subjected to moderate water stress, improving their physiological state. The use of these bacteria in agricultural production systems could reduce the amount of water for agricultural irrigation without having a negative impact on food production.
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Garcia-Oliva, Cecilia, Pilar Hoyos, Lucie Petrásková, Natalia Kulik, Helena Pelantová, Alfredo H. Cabanillas, Ángel Rumbero, Vladimír Křen, María J. Hernáiz und Pavla Bojarová. „Acceptor Specificity of β-N-Acetylhexosaminidase from Talaromyces flavus: A Rational Explanation“. International Journal of Molecular Sciences 20, Nr. 24 (07.12.2019): 6181. http://dx.doi.org/10.3390/ijms20246181.
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Fungal β-N-acetylhexosaminidases, though hydrolytic enzymes in vivo, are useful tools in the preparation of oligosaccharides of biological interest. The β-N-acetylhexosaminidase from Talaromyces flavus is remarkable in terms of its synthetic potential, broad substrate specificity, and tolerance to substrate modifications. It can be heterologously produced in Pichia pastoris in a high yield. The mutation of the Tyr470 residue to histidine greatly enhances its transglycosylation capability. The aim of this work was to identify the structural requirements of this model β-N-acetylhexosaminidase for its transglycosylation acceptors and formulate a structure–activity relationship study. Enzymatic reactions were performed using an activated glycosyl donor, 4-nitrophenyl N-acetyl-β-d-glucosaminide or 4-nitrophenyl N-acetyl-β-d-galactosaminide, and a panel of glycosyl acceptors of varying structural features (N-acetylglucosamine, glucose, N-acetylgalactosamine, galactose, N-acetylmuramic acid, and glucuronic acid). The transglycosylation products were isolated and structurally characterized. The C-2 N-acetamido group in the acceptor molecule was found to be essential for recognition by the enzyme. The presence of the C-2 hydroxyl moiety strongly hindered the normal course of transglycosylation, yielding unique non-reducing disaccharides in a low yield. Moreover, whereas the gluco-configuration at C-4 steered the glycosylation into the β(1-4) position, the galacto-acceptor afforded a β(1-6) glycosidic linkage. The Y470H mutant enzyme was tested with acceptors based on β-glycosides of uronic acid and N-acetylmuramic acid. With the latter acceptor, we were able to isolate and characterize one glycosylation product in a low yield. To our knowledge, this is the first example of enzymatic glycosylation of an N-acetylmuramic acid derivative. In order to explain these findings and predict enzyme behavior, a modeling study was accomplished that correlated with the acquired experimental data.