Dissertations / Theses: 'Triosephosphate isomerases'

1

Yüksel, K. Umit. "Molecular Aging of Triosephosphate Isomerase." Thesis, North Texas State University, 1987. https://digital.library.unt.edu/ark:/67531/metadc935641/.

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2

Alahuhta, M. (Markus). "Protein crystallography of triosephosphate isomerases: functional and protein engineering studies." Doctoral thesis, University of Oulu, 2008. http://urn.fi/urn:isbn:9789514287909.

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Abstract The aim of this PhD-study was to better understand the structure-function relationship of triosephosphate isomerase (TIM) and to use this expertise to change its substrate specificity. TIM is an important enzyme of the glycolytic pathway which catalyzes the interconversion of D-glyceraldehyde phosphate (D-GAP) and dihydroxyacetone phosphate (DHAP). Two main subjects are discussed: the engineering of monomeric TIM to create new substrate specificity and the structure-function relationship studies of the catalytically important mobile loop6. The starting point for the protein engineering project was the monomeric ml8bTIM, with an extended binding pocket between loop7 and loop8. Rational protein engineering efforts have resulted in a new variant called A-TIM that can competently bind wild type transition state analogues. A-TIM was also able to bind citrate, a compound that the wild type TIM does not bind. This A-TIM citrate complex structure is a good starting point for future protein engineering efforts. Based on the assumption that it would be beneficial for the monomeric forms of TIM to have loop6 closed permanently to increase the population of competent active sites, two point mutation variants, A178L and P168A were generated and characterized. The A178L-mutation was made to favor the closed conformation of loop6 through steric clashes in the open conformation. The P168A variant was made to stabilize the closed conformation of loop6 by removing strain. The A178L mutation induced some features of the closed conformation, but did not result in a closed conformation in the absence of ligands. Our structural studies also show that the P168A mutation does not favor the closed conformation either. However, the structures of the unliganded and liganded P168A variant, together with other known TIM structures show that the substrate binding first induces closure of loop7. This conformational switch subsequently forces loop6 to adopt its closed conformation. The protein engineering project was successful, but the efforts to find variants with a permanently closed loop6 did not fully succeed. In the context of this thesis a monomeric variant of TIM, with new binding properties, was created. Nevertheless, A-TIM still competently binds the inhibitors and transition state analogues of wild type TIM. Also, when combined, results discussed in the context of this thesis indicate that in wild type TIM the closure of loop7 after ligand binding is the initial step in the series of conformational changes that lead to the formation of the competent active site
Tiivistelmä Tämän väitöskirjatyön tarkoituksena oli oppia paremmin ymmärtämään trioosifosfaatti-isomeraasin (TIM) toimintamekanismeja sen rakenteen perusteella ja käyttää tätä tietämystä samaisen proteiinin muokkaamiseen uusiin tarkoituksiin. TIM on keskeinen entsyymi solun energian tuotannossa ja sen toiminta on välttämätöntä kaikille eliöille. Tämän vuoksi on tärkeää oppia ymmärtämään miten se saavuttaa tehokkaan reaktionopeutensa ja miksi se katalysoi vain D-glyseraldehydi-3-fosfaattia (D-GAP) ja dihydroksiasetonifosfaattia (DHAP). TIM:n toiminta mekanismien ymmärtämiseksi sen aminohapposekvenssiä muokattiin kahdesta kohtaa (P168A ja A178L) ja seuraukset todettiin mittaamalla tuotettujen proteiinien stabiilisuutta optisesti eri lämpötiloissa ja selvittämällä niiden kolmiulotteinen rakenne käyttäen röntgensädekristallografiaa. Mutaatioita tehtiin dimeeriseen villityypin TIM:in (wtTIM) ja jo aikaisemmin muokattuun monomeeriseen TIM:in (ml1TIM). Näiden mutaatioiden tarkoituksena oli suosia entsyymin aktiivista konformaatiota, jossa reaktion kannalta välttämätön vapaasti liikkuva peptidisilmukka numero 6 on suljetussa konformaatiossa. Monomeerisissä TIM:ssa peptidisilmukka numero 6:n ei ole välttämätöntä aueta. Tulokset mutaatiokokeista olivat osittain lupaavia. P168A-mutaatio lisäsi D-GAP:in sitoutumista, mutta rikkoi tärkeän mekanismin suljetussa, ligandia sitovassa, konformaatiossa. A178L-mutaatio aiheutti muutoksia avoimeen konformaatioon ja teki siitä suljettua konformaatiota muistuttavan jopa ilman ligandia, mutta samalla koko proteiini muuttui epävakaammaksi. Näistä kahdesta mutaatiosta A178L voisi olla hyödyllinen muokattujen TIM-versioiden ominaisuuksien parantamiseksi. Lisäksi yhdessä jo aikaisemmin julkaistujen yksityiskohtien kanssa nämä tulokset tekevät mahdolliseksi esittää tarkennusta siihen miten TIM toimii kun ligandi saapuu sen lähettyville. Tämän väitöskirjatyön yksi tavoite oli myös muokata edelleen monomeeristä TIM versiota (ml8bTIM), joka on suunniteltu siten, että se voi mahdollisesti sitoa uudenlaisia ligandeja. Tämä projekti vaati onnistuakseen 20 eri versiota ml8bTIM:n sekvenssistä ja noin 30 rakennetta. Uusia ligandeja sitova muoto (A-TIM) sitoi onnistuneesti sitraattia ja villityypin TIM:n inhibiittoreita. Erityisen lupaavaa oli, että A-TIM sitoi myös bromohydroksiasetonifosfaattia (BHAP), joka sitoutuu ainoastaan toimivaan aktiiviseen kohtaan. Nämä tulokset osoittavat, että A-TIM kykenee tarvittaessa katalysoimaan isomerisaatio reaktion uudenlaisille molekyyleille. Esimerkiksi katalysoimaan isomerisointireaktiota sokerianalogien tuotannossa

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3

Craig, Leonard C. (Leonard Callaway). "Analysis of a Human Transfer RNA Gene Cluster and Characterization of the Transcription Unit and Two Processed Pseudogenes of Chimpanzee Triosephosphate Isomerase." Thesis, University of North Texas, 1990. https://digital.library.unt.edu/ark:/67531/metadc331579/.

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An 18.5-kb human DNA segment was selected from a human XCharon-4A library by hybridization to mammalian valine tRNAiAc and found to encompass a cluster of three tRNA genes. Two valine tRNA genes with anticodons of AAC and CAC, encoding the major and minor cytoplasmic valine tRNA isoacceptors, respectively, and a lysine tRNAcuu gene were identified by Southern blot hybridization and DNA sequence analysis of a 7.1-kb region of the human DNA insert. At least nine Alu family members were found interspersed throughout the human DNA fragment. The tRNA genes are accurately transcribed by RNA polymerase III in a HeLa cell extract, since the RNase Ti fingerprints of the mature-sized tRNA transcription products are consistent with the DNA sequences of the structural genes. Three members of the chimpanzee triosephosphate isomerase (TPI) gene family, the functional transcription unit and two processed pseudogenes, were characterized by genomic blotting and DNA sequence analysis. The bona fide TPI gene spans 3.5 kb with seven exons and six introns, and is the first complete hominoid TPI gene sequenced. The gene exhibits a very high identity with the human and rhesus TPI genes. In particular, the polypeptides of 248 amino acids encoded by the chimpanzee and human TPI genes are identical, although the two coding regions differ in the third codon wobble positions for five amino acids. An Alu member occurs upstream from one of the processed pseudogenes, whereas an isolated endogenous retroviral long terminal repeat (HERV-K) occurs within the structural region of the other processed pseudogene. The ages of the processed pseudogenes were estimated to be 2.6 and 10.4 million years, implying that one was inserted into the genome before the divergence of the chimpanzee and human lineages, and the other inserted into the chimpanzee genome after the divergence.

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4

Krause, Mirja [Verfasser], Peter [Akademischer Betreuer] Neubauer, Rik [Akademischer Betreuer] Wierenga, and Juri [Akademischer Betreuer] Rappsilber. "Creating artificial sugar isomerases on the scaffold of a monomeric triosephosphate isomerase (A‐TIM) by protein engineering / Mirja Krause. Gutachter: Peter Neubauer ; Rik Wierenga ; Juri Rappsilber. Betreuer: Peter Neubauer ; Rik Wierenga." Berlin : Technische Universität Berlin, 2014. http://d-nb.info/1065665962/34.

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5

Lolis, Elias. "Crystallography and mutogenesis triosephosphate isomerase." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/13959.

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6

Chang, Timothy C. "Evaluating the Role of Glu97 in Triosephosphate Isomerase." Thesis, California State University, Long Beach, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10979019.

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A comprehensive understanding of the design of proteins puts heavy emphasis on certain key residues. These key residues can often be identified by the level of conservation in nature, which acts as a reliable witness mark in order to study the pressures that select for residues which play a critical role in the function of the protein. In the case of triosephosphate isomerase (TIM), the fifth enzyme in glycolysis, the second-shell residue Glu97 has been found to be fully conserved across all known TIM sequences. Its proximity to the active site as well as several previous studies has pointed to a possible direct role in catalysis. However, the present study shows when Glu97 is mutated to Ala, Gln, and Asp in Trypanosoma brucei brucei (tbb) that the resulting effects on k_cat are small. Previous results from other studies that have observed larger mutational effects may be due to nearby non-conserved residues that are specific to the TIM homolog in which these studies are performed. The structural studies detailed here suggest that instead, Glu97 is involved in the structural stability of the enzyme, as well as participating in dimer formation. Size-exclusion chromatography analysis suggests that several tbbTIM mutants may in fact be monomeric.

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7

Fugtong, Nantana. "Physiological consequences of triosephosphate isomerase overproduction in Saccharomyces cerevisiae." Thesis, University of Edinburgh, 1995. http://hdl.handle.net/1842/20513.

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Triosephosphate isomerase was overproduced in yeast Saccharomyces cerevisiae by integration of extra copies of the TPI1 gene into the yeast chromosome. Specific enzyme activity was found to have increased between 2-7 fold above the wild-type level depending on the isolate used. The physiological consequences of enzyme overproduction by a factor of 2 and 7 were studied in aerobic batch cultures and aerobic glucose-limited chemostat cultures. Batch cultivation indicated that no significant difference in growth and metabolite production between overproducers and the reference could be detected. However, lower levels of three other glycolytic enzymes (PGK, PYK and HK) were found in a 7-fold TPI overproducer. Dilution rate profiles of TPI overproducers and the reference were studied in glucose-limited chemostat culture. The 7-fold TPI overproducer showed ethanol formation at D = 0.11 h^-1 where the 2-fold overproducer and the reference did not produce ethanol at all. Increase in dilution rate to 0.32 h^-1 resulted in increases of ethanol production rate as well as the rates of pyruvate and acetate production. The much more sensitive competitive chemostat cultures between TPI overproducers (2-fold or 7-fold) and the reference strain were studied using LEU2 gene as a detectable marker. The marker, however, showed strong effects on selection under all competitive chemostat studies. TPI activity was therefore used as a measure to determine the proportion of the strains in competition between the reference and TPI overproducers. Results showed that the 7-fold TPI overproducer was slightly favoured when competed against the 2-fold overproducer. However, this strain was found to be inferior to the reference strain. This is discussed as a possible effect of differences in URA3 gene copy number carried in these strains.

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8

Sun, An-Qiang. "How Do Enzymes Wear Out? Effects of Posttranslational Modifications on Structure and Stability of Proteins; The Triosephosphate Isomerase Model." Thesis, University of North Texas, 1991. https://digital.library.unt.edu/ark:/67531/metadc798116/.

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Triosephosphate isomerase (EC 5.3.1.1., TPI) undergoes specific posttranslational modifications (deamidation and oxidation) which are believed to initiate protein turnover by destabilization of the dimer. The crystal structures, amino acid sequences, and aging related changes of TPI from various species have been independently characterized by several laboratories. TPI has thus become the prototype enzyme for examining the initial steps in protein turnover. The binding of substrate enhances the specific deamidation of the mammalian enzyme, and a general mechanism of 'molecular wear and tear' [Gracy, R. W., Yiiksel, K. 0., Chapman, M. L., and Dimitrijevich, S. D. (1990) in Isozymes-Structure, Function and Use in Biology and Medicine (Ogita, Z-I., and Markert, C. L., Eds) pp. 787-817, Wiley-Liss, New York] has been proposed to explain how enzymes may wear out.

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9

Kursula, I. (Inari). "Crystallographic studies on the structure-function relationships in triosephosphate isomerase." Doctoral thesis, University of Oulu, 2003. http://urn.fi/urn:isbn:9514270096.

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Abstract The triosephosphate isomerase (TIM) barrel superfamily is a broad family of proteins, most of which are enzymes. At the amino-acid-sequence level, many of the members of this family share little, if any, homology. Yet, they adopt the same three-dimensional (βα)8 fold. The TIM barrel fold seems to be a good framework for many different kinds of enzymes, providing unique possibilities for both natural and human-designed evolution, as the catalytic center and the stabilizing features are separated to different ends of the barrel. Indeed, in the light of most recent studies, it seems likely that at least most of the different TIM barrel enzymes, catalyzing a huge variety of reactions, have evolved from a common ancestor. TIM can be considered a real text-book enzyme — its catalytic properties and stucture-function relationships have been studied for decades. Still, at present, we are quite far from understanding the structural features that make TIM and other enzymes such superior catalysts in both efficiency and precision. TIM is a dimeric enzyme that consists of two identical subunits of 250 residues. It catalyzes the interconversion of dihydroxyacetone phosphate and D-glyceraldehyde-3-phosphate in glycolysis. The basics of this reaction are well known, but there is ongoing discussion about the details of the proton transfer steps, and three alternative pathways have been suggested. In addition, it is a fascinating question how the enzyme succeeds in abstracting a highly stable proton from a carbon atom of the substrate. This study was undertaken to shed light on some of the questions concerning the structure-function relationships in TIM. The most important findings are the elucidation of the role of Asn11 as a catalytic residue and the meaning of the flexibility of both the catalytic Glu167 side chain as well as the substrate during catalysis, and the presence of a low-barrier hydrogen bond between Glu167 and a transition-state analogue, 2-phosphoglycolate. Furthermore, significant results were obtained on the importance of a conserved salt bridge, 20 Å away from the active site and the dimer interface, for the stability and folding of TIM as well as on the factors influencing the opening of the flexible loop 6 upon product release.

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10

Colquhoun, Anh N. "Investigating the Role of Glutamate 97 in Triosephosphate Isomerase from Homo sapiens." Thesis, California State University, Long Beach, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10976077.

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In spite of the advances made in experimental and mutational studies, understanding the importance of remote interactions is crucial for refining the knowledge of enzyme catalysis. In this study, a model system for Glu97 was developed in Homo sapiens triosephosphate isomerase ( hTIM) to investigate the energetic contribution and structural role of this fully conserved glutamate residue in the TIM-catalyzed isomerization reaction. Recombinant human triosephosphate isomerase (hTIM) was altered using site-directed mutagenesis, in which an aspartate, glutamine, or alanine residue was substituted for Glu97. In steady-state kinetics, the E97D variant exhibited the most significant catalytic activity while the E97Q enzyme was the least active. Observing both the forward and reverse directions of the TIM-catalyzed reaction, the results revealed that the enzymatic activity for E97D and E97A TIM was diminished by ~3-fold or less, and the rate was essentially unchanged for the E97D mutation. The E97Q mutant observed a greater rate effect, ~10-fold decrease in k_cat and ~20-fold decrease in catalytic efficiency (kcat/ K_M). To determine the conformational stability of the WT and mutant hTIM, unfolding of all four enzymes was monitored by circular dichroism, tryptophan and ANS fluorescence spectroscopy. The dimer stability was evaluated by gel-filtration analysis and the mutants showed similar chromatograms compared to that of the WT. The similar behavior observed for the WT and E97D suggests that the Asp mutation has little effect on catalysis, enzyme stability, and the unfolding pathway. On the contrary, the statistical significance observed in the E97Q and E97A mutants suggests that the Gln and Ala mutations affect the stability of the structure and may affect the unfolding pathway. Overall, these point-mutations support the model that remote interactions of Glu97 may have a modest role in catalysis. One explanation is that the direct role of Glu97 may have evolved in the human species and plays a less significant role compared to earlier species in evolution in which Glu97 mutations showed larger rate effects. Possibly, the network of unfavorable interactions is reduced and therefore, the mutational effect of Glu97 is less deleterious in hTIM.

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11

Humphries, Ann Louise. "The origin and significance of mutation in the triosephosphate isomerase (TPI) gene promoter." Thesis, King's College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325543.

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12

Mohan, Sidharth. "Consensus, Correlation And Combinatorics Based Approaches In Engineering And Exploring Triosephosphate Isomerase Stability." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1503054678218166.

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13

Witmans, Cornelis Jacobus. "An approach to the rational design of new inhibitors for Trypanosoma brucei Triosephosphate isomerase /." [S.l. : [Groningen] : s.n.] ; [University Library Groningen] [Host], 1995. http://irs.ub.rug.nl/ppn/139946616.

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14

Seangmany, Nessa. "Evaluating the role of a conserved residue in triosephosphate isomerase from Trypanosoma brucei brucei." Thesis, California State University, Long Beach, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10159003.

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A distinguishing feature of enzymatic catalysis in comparison to small-molecule catalysts is that enzymes use non-covalent interactions to position substrates and active site residues relative to each other. Although residues implicated in positioning can be readily identified by structural inspection, understanding the catalytic importance of these interactions requires experimental tests. Enzyme active sites often contain networks of interactions for which the functional role cannot be distinguished by the structure alone. In triosephosphate isomerase (TIM), a key enzyme in glycolysis, structural and mutational results suggest an important catalytic role for three active site residues: Lys13, His95, and Glu167. A glutamate residue (Glu97) has been shown to be conserved in almost all species of TIM. Based on X-ray structures, a potential role of Glu97 may be to position Lys13. To investigate the role of Glu97 in TIM catalysis, we mutated Glu97 to Ala, Gln, and Asp in Trypanosoma brucei brucei. The Glu97Ala, Glu97Gln, and Glu97Asp mutations led to an ~10,000-fold, ~40-fold, and ~10-fold reduction in k_cat respectively. The similar K_M value in Glu97Gln and Glu97Asp mutations relative to wild-type TIM suggests substrate binding is not affected by the mutation. The Glu97Ala mutation led to a slight increased K_M relative to wild-type, suggesting that Glu97 may play a role in maintaining the structural stability of TIM. Circular dichroism analysis shows that the E97 mutations do not affect the overall helical structure of TIM. Overall, the results provide evidence for this non-active site residue playing an important role in TIM catalysis.

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15

Khoury, Chris B. "Evaluating the Structural Role of a Conserved Glutamate Residue in Triosephosphate Isomerase from Trypanosoma brucei brucei." Thesis, California State University, Long Beach, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10604764.

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It is well known that enzymes differ from small-molecule catalysts by use of non-covalent interactions to position active site residues, but our understanding of the relative importance of residues in this positioning is limited. Active site residues participate directly in covalent and non-covalent interactions with substrates, but second shell residues may also contribute indirectly to catalysis through positioning and structuring. In triosephosphate isomerase (TIM), a key glycolytic enzyme, a highly conserved glutamate residue at position 97 has been suggested to be important for catalysis and may be important for positioning a key active site lysine residue (K13). In Trypanosoma brucei brucei (TBB), a kinetoplastid which causes African sleeping sickness, Glu97 has been shown to be catalytically important. Mutations of Glu97 to Gln, Asp and Ala have been shown to lead to approximate 24-, 18-, and 6280-fold k_cat decreases, respectively. Whereas this glutamate residue is involved in the catalysis of the enzyme, the nature of its involvement in the structure of the enzyme is unclear. To evaluate the role of this residue in the structure of the enzyme, we performed structural and denaturation evaluations using intrinsic and ANS fluorescence. Our results suggested that the Glu97Asp and Glu97Gln mutations did not significantly perturb the structure of the enzyme compared with the wild-type, but may have slight structural effects, based on spectral center of mass and λ_max values. Denaturation evaluations suggested that the Glu97Asp and Glu97Gln did not significantly destabilize the enzyme based on [GdnHCl]1/2. The effect of the Glu97Ala mutation, however, was less clear. Overall, our results suggested that although Glu97 is important to catalysis, Glu97Asp and Glu97Gln mutants do not appear to significantly perturb structure, but may have slight effects. Future directions include continued investigation of Glu97Ala, and evaluation of the structural effects of double mutants at the Glu97 and Lys13 positions.

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16

Sullivan, Brandon Joseph. "Engineering Proteins from Sequence Statistics: Identifying and Understanding the Roles of Conservation and Correlation in Triosephosphate Isomerase." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1325106135.

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17

De, Moor Warren Ralph Josephus. "The interaction of silver nanoparticles with triosephosphate isomerase from human and malarial parasite (Plasmodium falciparum) : a comparative study." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1020895.

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The advent of advanced modern nanotechnology techniques offers new and exciting opportunities to develop novel nanotech-derived antimalarial nanodrugs with enhanced selective and targeting abilities that allow for lower effective drug dosages, longer drug persistence and reduced drug degradation within the body. Using a nanodrug approach also has the advantage of avoiding drug resistance problems that plague reconfigured versions of already-existing antimalarial drugs. In this study recombinant triosephosphate isomerase enzymes from Plasmodium falciparum (PfTIM) and Humans (hTIM) were recombinantly expressed, purified and characterised. PfTIM was shown to have optimal pH stability at pH 5.0-5.5 and thermal stability at 25°C with Km 4.34 mM and Vmax 0.876 μmol.ml⁻ₑmin⁻ₑ. For hTIM, these parameters were as follows: pH optima of 6.5-7.0; temperature optima of 30°C, with Km 2.27 mM and Vmax 0.714 μmol.ml⁻ₑmin⁻ₑ. Recombinant TIM enzymes were subjected to inhibition studies using polyvinylpyrrolidone (PVP) stabilised silver nanoparticles (AgNPs) of 4-12 nm in diameter. These studies showed that the AgNPs were able to selectively inhibit PfTIM over hTIM with an 8-fold greater decrease in enzymatic efficiency (Kcat/Km) observed for PfTIM, as compared to hTIM, for kinetics tests done using 0.06 μM of AgNPs. Complete inhibition of PfTIM under optimal conditions was achieved using 0.25 μM AgNPs after 45 minutes while hTIM maintained approximately 31% of its activity at this AgNP concentration. The above results indicate that selective enzymatic targeting of the important, key metabolic enzyme TIM, can be achieved using nanotechnology-derived nanodrugs. It was demonstrated that the key structural differences, between the two enzyme variants, were significant enough to create unique characteristics for each TIM variant, thereby allowing for selective enzyme targeting using AgNPs. If these AgNPs could be coupled with a nanotechnology-derived, targeted localization mechanism – possibly using apoferritin to deliver the AgNPs to infected erythrocytes (Burns and Pollock, 2008) – then such an approach could offer new opportunities for the development of viable antimalarial nanodrugs. For this to be achieved further research into several key areas will be required, including nanoparticle toxicity, drug localization and testing the lethality of the system on live parasite cultures.

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18

Dantu, Sarath Chandra [Verfasser], Kai [Akademischer Betreuer] Tittmann, Burkhard [Akademischer Betreuer] Morgenstern, and Gerrit [Akademischer Betreuer] Groenhof. "Conformational Sampling of Enzyme dynamics: Triosephosphate Isomerase / Sarath Chandra Dantu. Gutachter: Kai Tittmann ; Burkhard Morgenstern ; Gerrit Groenhof. Betreuer: Kai Tittmann." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://d-nb.info/1044767413/34.

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19

Vaismaa, M. (Matti). "Development of benign synthesis of some terminal α-hydroxy ketones and aldehydes." Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514291753.

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Abstract The synthesis of α-hydroxy aldehydes and hydroxymethyl ketones as well as their interconversion to each other are discussed in this thesis. The literature survey of the monograph reviews the synthetic methods for the preparation of 1,2-bifunctionalized hydroxy aldehydes and ketones. The keto-aldehyde isomerisation reaction catalyzed by Triosephosphate isomerase enzyme (TIM) and organic compounds that interact with the TIM are also introduced. In addition, the microwave heating techniques in organic syntheses are reviewed. The practical work consists of two entities: The synthesis of new substrate candidates and transition state analogues for a mutated monomeric TIM. These compounds are model compounds for the catalytic activity and the structural studies of the mutated monomeric TIM. The synthesis of the sulphonyl α-hydroxy ketone-based substrate candidates consists of four successive syntheses. The microwave-activation was utilized in the preparation of a carbon-sulphur bond and the synthesis of hydroxymethyl ketones. The improved synthesis of the terminal α-hydroxy ketone functionality with microwave activation is presented. The formation of charged compounds was utilized to improve the absorption of microwave energy of reaction mixtures. The design and the synthetic work were carried out in accordance to principles of green chemistry. The second part of the practical work is the development of an organocatalytic α-oxybenzoylation reaction of aldehydes with high enantiomeric selectivity. This novel method generated enantiomerically pure α-hydroxy aldehydes in the stable benzoate-protected form from achiral starting materials under mild conditions at the presence of air and moisture.

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20

Abdulla, Sheera. "Biochemical characterisation of unusual glycolytic enzymes from the human intestinal parasite Blastocystis hominis." Thesis, University of Exeter, 2016. http://hdl.handle.net/10871/23933.

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Blastocystis is an important parasite that infects humans and a wide range of animals like rats, birds, reptiles, etc. infecting a sum of 60% of world population. It belongs to the Stramenopiles, a Heterologous group that includes for example the Phythophthora infestans the responsible for the Irish potato famine. Previous work had reported the presence of an unusual fusion protein that is composed of two of the main glycolytic enzymes; Triosephosphate isomerase-glyceraldehyde-3-phosphate dehydrogenase (TPI-GAPDH). Little is known about this protein. Blastocystis TPI-GAPDH and Blastocystis enolase were both characterized biochemically and biophysically in this project. The phylogenetic relationships of those two proteins among other members of either Stramenopiles, or other members of the kingdom of life were examined and found to be grouping within the chromalveolates. Our studies revealed that those two proteins, Blastocystis enolase and Blastocystis TPI-GAPDH, had a peptide signal targeting them to the mitochondria. This was an unusual finding knowing that text books always referred to the glycolytic pathway as a canonical cytoplasmic pathway. Structural studies had also been conducted to unravel the unknown structure of the fusion protein Blastocystis TPI-GAPDH. X-ray crystallography had been conducted to solve the protein structure and the protein was found to be a tetrameric protein composed of a central tetrameric GAPDH protein flanked with two dimmers of TPI protein. Solving its structure would be the starting point towards reviling the role that TPI-GAPDH might play in Blastocystis and other organisms that it was found in as well. Although a fusion protein, the individual components of the fusion were found to contain all features deemed essential for function for TPI and GAPDH and contain all expected protein motifs for these enzymes.

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21

Ugur, Ilke. "Étude de la réaction de déamidation dans l'enzyme triosephosphate isomérase au moyen d'outils de calculs en chimie." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0020/document.

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La déamidation est la modification post-traductionnelle de l'asparagine (Asn) et de la glutamine (Glu). Elle est communèment observée dans les peptides et les protéines. Il a été démontré que la déamidation limite la durée de vie de ces macromolécules. Dans ce travail, la déamidation de l'asparagine dans des petits peptides et dans l'enzyme triosephosphate isomérase a été modélisée. La déamidation dans la triosephosphate isomérase de mammifères a été observée sur deux sites distincts: Asn15 et Asn71. Asn71 a une vitesse de déamidation plus élevée que Asn15 et moins grande que pour un petit peptide. Il a été suggéré que la déamidation de Asn15 se produit sous l'influence de la déamidation de Asn71. Pour expliquer ces résultats expérimentaux, des simulations de dynamiques moléculaires classiques à l'échelle de la microseconde et des calculs d'énergie libre, de type umbrella sampling, à l'aide de méthodes combinées mécanique quantique/mécanique moléculaire ont été réalisés. Nous montrons que la déamidation séquentielle dans la triosephosphate isomérase est due à la fois à des effets locaux et globaux. Ces résultats apporte une nouvelle perspective sur l'impact de l'ordre structurel sur la vitesse de déamidation Nous avons également déterminé la voie la plus plausible de cette reaction ainsi que l'influence de la variation du pKa, dans la chaîne principale, de la partie amide du résidu adjacent de l'asparagine sur la vitesse de déamidation. En regard de l'importance des variations de pKa dans l'environnement protéique, nous avons élaboré un protocole informatique permettant d'évaluer de manière rapide et précise des pKa . Ce protocole a été appliqué à des petites molécules organiques et nous avons montré qu'il était également applicable à des études relatives à la prédiction de pKa dans les protéines
Deamidation is the posttranslational modification of asparagine (Asn) and glutamine (Glu) residues, which is observed in several proteins and peptides. It has been shown that deamidation limits the lifetime of these macromolecules. In this work, deamidation of asparagine in small peptides and in the enzyme triosephosphate isomerase has been modeled. Deamidation in mammalian triosephosphate isomerase has been observed at two distinct deamidation sites: Asn15 and Asn71. Asn71 deamidates faster than Asn15 and slower than a small peptide. It has been suggested that, deamidation at Asn15 occurs with the influence of deamidated Asn71. In order to explain these experimental findings, microsecond long classical molecular dynamics simulations and free energy calculations using quantum mechanics/molecular mechanics tools combined with umbrella sampling technique have been performed. The sequential deamidation in triosephosphate isomerase has been shown to be related with both global and local effects. These results bring a new perspective to the impact of the high-order structure on deamidation rate. The most plausible route of this reaction was also determined. The pKa shift of backbone amide of the residue adjacent to asparagine has been found to be one of the most crucial factor determining the rate of deamidation. Considering the importance of pKa shifts in protein environment, a computational protocol was suggested in order to obtain accurate and fast pKa predictions. This protocol was applied to small organic molecules, and it has been shown to be applicable to studies concerning aminoacid pKa predictions

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22

Casteleijn, M. G. (Marinus G. ). "Towards new enzymes:protein engineering versus bioinformatic studies." Doctoral thesis, University of Oulu, 2010. http://urn.fi/urn:isbn:9789514260995.

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Abstract The aim of this PhD-study was to address some of the overlapping bottlenecks in protein engineering and metagenomics by developing or applying new tools which are useful for both disciplines. Two enzymes were studied as an example: Triosephosphate Isomerase (TIM) and Uridine Phosphorylase (UP). TIM is an important enzyme of the glycolysis pathway and has been investigated via means of protein engineering, while UP is a key enzyme in the pyrimidine-salvage pathway. In this thesis TIM was used to address protein engineering aspects, while UP was used in regards to some metagenomic and bioinformatic aspects. The aspects of a structural driven rational design approach and its implications for further engineering of monomeric TIM variants are discussed. Process development based on a new technology, EnBase®, addresses the relative instability of new variants, compared to its ancestors, for further studies. EnBase® is then applied for the production of 15N isotope labeling of a monomeric TIM variant, A-TIM. Systematical function- and engineering studies on dimeric TIM and monomeric TIM in regards to the hinges of the catalytic loop-6 were conducted to investigate enzyme activity and stability. Both the A178L and P168A were proposed to induce loop-6 closure, a wanted feature for A-TIM variants. The P168A mutants are hardly active, but gave great insight into the catalytic machinery, while the A178L mutants did induce partial loop-6 closure, however in addition, monomeric A178L was destabilized. Homology driven genome mining and subsequent isolation- high throughput (HTP) overexpression of a thermostable UP from the Archaea Aeopyrum pernix was carried out as an example for the production of recombinant proteins. In addition an alternative kinetic method to study the kinetics of UP by means of NMR directly from cell lysate is discussed. The combination of expression libraries and EnBase® in a HTP manner may relieve up the gene-to-product bottleneck. The structural aspects of A. pernix UP are explored by means of simple bioinformatic tools in the last section of this thesis. A thermostable, truncated version of UP was created and its use for protein engineering in the future is explored. The long N-terminal and C-terminal ends of A. pernix UP seem to be involved in stabilizing the dimeric and hexameric structures of UP. However, deletion of the N-terminal end of A. pernix UP yielded a thermostable protein. Overall, the finding in regards to process optimization and HTP expression and optimization and the underlying methods used in the TIM studies and the UP studies are interchangeable.

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23

Penteado, Renato Ferras. "ESTUDOS ESTRUTURAIS POR CRISTALOGRAFIA E MODELAGEM COMPUTACIONAL DA LIPASE DE PINHÃO MANSO (Jatropha curcas) E DA TRIOSE FOSFATO ISOMERASE DE Naegleria gruberi." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2016. http://tede2.uepg.br/jspui/handle/prefix/2047.

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Made available in DSpace on 2017-07-24T19:37:55Z (GMT). No. of bitstreams: 1 Renato Ferraz Penteado.pdf: 5510615 bytes, checksum: a1e326883a6f1e7ad0decd6835add201 (MD5) Previous issue date: 2016-08-09
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Knowledge of protein structures is of huge importance, since this information allows to understand the mechanisms through which proteins carry out their biological functions. Lipases constitute an enzymatic family capable to perform synthesis or hydrolysis of ester bonds of triacyl glycerols (TAGs) with long chain fatty acids.These enzymes are the theme of many investigations given their potential to be used in a wide variety of apllications involving chemicals with the ester functional group,e.g., in organic synthesis. On the other hand, structural knowledge of some enzymes is important for the development of new therapeutic drugs or even to contribute for the understanding of structural evolutionary features, like those belonging to metabolic pathways. In this work were accomplished the homology modeling of the lipase from Jatropha curcas and the structure determination of the triosephosphate isomerase from Naegleria gruberi from three X ray diffraction data sets. Among three experimental structures obtained, two belong to C2 space group, with different unit cells, and one to P4122 space group. Initial phases were obtained by molecular replacement procedure using the Phaser program and all structures were refined interactively with Coot and Phenix programs. In one structure it was possible to model three molecules of the precipitant agent Jeffamine present in the crystallization solution and one molecule of Tris buffer (placed at the active site). Structural comparisons were performed among the refined and validated model and some of its homologues, taking into account the differences observed in the structural-based alignment among them and characteristics noticed during the refinement procedure. Circular dichroism experiments have shown that thermal denaturation is irreversible to triosephosphate isomerase of Naegleria gruberi.
O conhecimento da estrutura de proteínas é de grande importância, uma vez que esta informação permite o entendimento dos mecanismos pelos quais elas desempenham suas funções biológicas. Lipases constituem uma família enzimática capaz de realizar a síntese ou hidrólise de ligações éster de substratos triacilgliceróis (TAGs) contendo ácidos graxos de cadeia longa. São alvo de muitos estudos dadas suas potencialidades em um grande número de aplicações envolvendo o grupo funcional éster, por exemplo, em química orgânica síntética. Já o conhecimento estrutural de algumas enzimas é importante para o desenvolvimento de novas drogas terapêuticas ou mesmo contribuir para o entendimento de aspectos evolutivos estruturais, como daquelas pertencentes a vias metabólicas. Neste trabalho foram realizadas a modelagem por homologia da estrutura lipase da planta Jatropha curcas e a determinação experimental da estrutura da triose fosfato isomerase do microrganismo Naegleria gruberi a partir de três conjuntos de imagens de difração de Raios X. Das três estruturas experimentais obtidas, duas pertencem ao grupo de espaço C2, com células unitárias diferentes, e uma ao grupo de espaço P4122. As fases iniciais foram obtidas com o procedimento de substituição molecular utilizando o programa PHASER e todas as estruturas foram refinadas iterativamente com o auxílio dos programas COOT e PHENIX. Em uma das estruturas foi possível modelar três moléculas do agente precipitante Jeffamine® presente na condição de cristalização e uma molécula do tampão Tris (no sítio ativo do monômero B). Comparações estruturais foram realizadas entre o modelo refinado e validado e algumas das proteínas homólogas, tendo em vista diferenças observadas no alinhamento baseado em estrutura entre elas e características notadas durante o procedimento de refinamento. Experimentos de dicroísmo circular mostraram que a desnaturação térmica é irreversível para esta proteína.

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24

Feierberg, Isabella. "Computational Studies of Enzymatic Enolization Reactions and Inhibitor Binding to a Malarial Protease." Doctoral thesis, Uppsala universitet, Institutionen för cell- och molekylärbiologi, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3335.

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Enolate formation by proton abstraction from an sp3-hybridized carbon atom situated next to a carbonyl or carboxylate group is an abundant process in nature. Since the corresponding nonenzymatic process in water is slow and unfavorable due to high intrinsic free energy barriers and high substrate pKa s, enzymes catalyzing such reaction steps must overcome both kinetic and thermodynamic obstacles. Computer simulations were used to study enolate formation catalyzed by glyoxalase I (GlxI) and 3-oxo-Δ5-steroid isomerase (KSI). The results, which reproduce experimental kinetic data, indicate that for both enzymes the free energy barrier reduction originates mainly from the balancing of substrate and catalytic base pKas. This was found to be accomplished primarily by electrostatic interactions. The results also suggest that the remaining barrier reduction can be explained by the lower reorganization energy in the preorganized enzyme compared to the solution reaction. Moreover, it seems that quantum effects, arising from zero-point vibrations and proton tunnelling, do not contribute significantly to the barrier reduction in GlxI. For KSI, the formation of a low-barrier hydrogen bond between the enzyme and the enolate, which is suggested to stabilize the enolate, was investigated and found unlikely. The low pKa of the catalytic base in the nonpolar active site of KSI may possibly be explained by the presence of a water molecule not detected by experiments. The hemoglobin-degrading aspartic proteases plasmepsinI and plasmepsin II from Plasmodium falciparum have emerged as putative drug targets against malaria. A series of C2- symmetric compounds with a 1,2-dihydroxyethylene scaffold were investigated for plasmepsin affinity, using computer simulations and enzyme inhibition assays. The calculations correctly predicted the stereochemical preferences of the scaffold and the effect of chemical modifications. Calculated absolute binding free energies reproduced experimental data well. As these inhibitors have down to subnanomolar inhibition constants of the plasmepsins and no measurable affinity to human cathepsin D, they constitute promising lead compounds for further drug development.

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25

Donnini, S. (Serena). "Computing free energies of protein-ligand association." Doctoral thesis, University of Oulu, 2007. http://urn.fi/urn:isbn:9789514285745.

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Abstract Spontaneous changes in protein systems, such as the binding of a ligand to an enzyme or receptor, are characterized by a decrease of free energy. Despite the recent developments in computing power and methodology, it remains challenging to accurately estimate free energy changes. Major issues are still concerned with the accuracy of the underlying model to describe the protein system and how well the calculation in fact emulates the behaviour of the system. This thesis is largely concerned with the quality of current free energy calculation methods as applied to protein-ligand systems. Several methodologies were employed to calculate Gibbs standard free energies of binding for a collection of protein-ligand complexes, for which experimental affinities were available. Calculations were performed using system description with different levels of accuracy and included a continuum approach, which considers the protein and the ligand at the atomic level but includes solvent as a polarizable continuum, and an all-atom approach that relies on molecular dynamics simulations. In most such applications, the effects of ionic strength are neglected. However, the severity of this approximation, in particular when calculating free energies of charged ligands, is not very clear. The issue of incorporating ionic strength in free energy calculations by means of explicit ions was investigated in greater detail and considerable attention was given to the affinities of charged peptides in the presence of explicit counter-ions. A second common approximation is concerned with the description of ligands that exhibit multiple protonation states. Because most of current methods do not model changes in the acid dissociation constants of titrating groups upon binding, protonation equilibria of such ligands are not taken into account in free energy calculations. The implications of this approximation when predicting affinities were analysed. Finally, when calculating free energies of binding, a correct description of the interactions between the protein and the ligand is of fundamental importance. However, active sites of enzymes, where strained conformations may hold a functional role, are not always accurately modelled by molecular mechanics force fields. The case of a strained planar proline in the active site of triosephosphate isomerase was investigated using an hybrid quantum mechanics/molecular mechanics method, which implies a higher level of accuracy.

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26

Dantu, Sarath Chandra. "Conformational Sampling of Enzyme dynamics: Triosephosphate Isomerase." Doctoral thesis, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-EF7C-9.

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Quinn, Caitlin. "Solid State NMR Relaxation Studies of Triosephosphate Isomerase." Thesis, 2013. https://doi.org/10.7916/D8H70P1T.

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Both protein structure and dynamics are essential to understanding biological function. NMR is a powerful technique for the observation of protein dynamics in that dynamics can be observed site-specifically over a wide range of timescales from picoseconds to seconds. Spin relaxation measurements, including relaxation in the rotating frame (R1ρ), can be very sensitive to exchange processes in proteins, particularly on the millisecond-to-microsecond timescale. Using solid state NMR, few techniques exist that can quantify dynamics on this timescale. Previous R1ρ relaxation measurements in the solid state have utilized reorientation of a dipole tensor to observe dynamics. This application is limited to systems where the nucleus of interest has an attached proton. Relaxation studies using the reorientation of a chemical shift tensor are applicable to a broader range of systems. Furthermore, solid state experiments do not require a change in the isotropic chemical shift as is necessary in solution NMR. We combined R1ρ measurements of the model compound dimethyl sulfone (DMS) with data-fitting routines in Spinevolution to show that R1ρ relaxation due to reorientation of a chemical shift tensor is a large effect in the solid state and these measurements can be used to quantify chemical exchange processes. The temperature dependence of the exchange rates determined with R1ρ measurements is in agreement with other measurements of the dynamics of DMS with various solid state NMR techniques. Deuteration and sparse isotropic labeling were necessary to obtain quantitative results. To distinguish the exchange contribution to relaxation from other effects (R2 relaxation), low temperatures and high spin-lock field strengths were utilized. R1ρ experiments and magic angle spinning (MAS) one-dimensional spectra were used to characterize phosphate ligand binding in the glycolytic protein triosephosphate isomerase. 1D spectra indicated the presence of both isotropic and anisotropic phosphate populations. These states included an unbound state with an isotropic chemical shift tensor, and a protein-bound state in which the anisotropic features are reintroduced through chelation with protein backbone amides. The chemical shift anisotropy tensor of the bound phosphate ligand was fit using spinning sideband analysis of slow MAS spectra and suggest the ligand is in a dianionic state. The temperature dependence of R1ρ measurements indicated a fast dynamic process above the microsecond timescale at physiological temperatures.

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28

Bandyopadhyay, Debarati. "Probing the Role of Highly Conserved Residues in Triosephosphate Isomerase : Biochemical & Structural Investigations." Thesis, 2015. http://etd.iisc.ernet.in/2005/3602.

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Conserved residues in protein are crucial for maintaining structure and function, either by direct involvement in chemistry or indirectly, by being essential for folding, stability and oligomerisation and are mostly clustered near active sites. The variability of sequences of the same protein from diverse organisms is a reflection of the selective pressures of evolution. Sequence conservation analysis with 3397 bacterial triosephosphate isomerase (TIM) sequences using Plasmodium falciparum (Pf) TIM as template, showed full conservation of ten residues, K12, T75, H95, E97, C126, E165, P166, G209, G210 and G228. The integrity of the enzyme active site, which lies near the dimer interface, makes TIM an obligatory dimer. Attempts to engineer active monomeric TIM have not been successful. The present study assesses the effects of mutations at fully conserved position 75 (Thr) and the highly conserved position 64 (Q: 3011, E: 383) near the dimer interface, using the recombinant Plasmodial enzyme. Residue 64, Gln in Pf, and T75 interact with the catalytic E97 and K12, respectively. Preliminary analysis of available crystal structures showed that Gln 64 takes part in a single intersubunit interaction and maintains the obligatory strained backbone angles of the catalytic K12 residue, while Thr 75 is involved in four intersusunit hydrogen bond interactions. This led to the hypothesis that mostly, Gln at position 64 is crucial for enzyme activity and Thr at position 75 for the integrity of the dimer. Biophysical and kinetic data are reported for four T75 (T75S/V/C/N) and two Q64 (Q64N/E) mutants. The major findings revealed that the mutations at position 64 have a significant effect on dimer integrity with a 1000 fold increase in the dimer dissociation constant compared to the wild type enzyme, while dimer stability was unimpaired for the T75 mutants. Concentration dependence of activity yielded an estimate of dimer dissociation constant (Kd) values (Q64N 73.7±9.2 nM and Q64E 44.6±8.4 nM). Enzyme activity values of the T75 mutants are comparable to the wild type, except for T75N which shows a 4-fold drop in activity. All four T75 mutants show a dramatic fall in activity between 35 °-45 °C. Crystal structure determination of the T75S/V/N mutant offers insights into the variation in local interactions with T75N showing the largest changes. These results were unanticipated emphasising the uncertainties involved in inferring functional and structural role for individual residues based only on analysis of interactions observed in crystal structures. Nanospray ionisation mass spectrometric studies has also been used to probe the oligomeric properties of the three mutant proteins Q64N, Q64E and T75S and the wild type enzyme in the gas phase. The gas phase distributions of dimeric and monomeric species have been examined under a wild range of collision energies (40 – 160 eV). The order in the gas phase, PfTIM wild type > T75S > Q64E ~ Q64N, together with the solution phase experiments described above establish the importance of Q64 and T75 in influencing stability and activity. Inhibition studies with a 27 residue synthetic dimer interface peptide and the Q64 mutants establish that the interaction between the protein and the peptide was facilitated in the case of monomeric species.

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29

Ray, Soumya S. "Structure, Stability And Unfolding Of Plasmodium falciparum Triosephosphate Isomerase." Thesis, 1999. http://etd.iisc.ernet.in/handle/2005/1540.

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Samanta, Moumita. "Exploring The Role Of The Highly Conserved Residues In Triosephosphate Isomerase." Thesis, 2011. http://etd.iisc.ernet.in/handle/2005/2366.

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This thesis discusses the structure-function studies on triosephosphate isomerase (TIM) from Plasmodium falciparum (Pf), directed towards understanding the roles of highly conserved residues by site derected mutagenesis. Chapter 1 provides an introductory overview to the relevant literature on triosephosphate isomerase. In addition, this Chapter provides an analysis of conserved residues in TIM, and amino acid diversity at specific positions in the structure using a dataset of 503 TIM sequences. Chapter 2 reports the work on the completely conserved residue, C126 in TIM, which is proximal to the active site. Five mutants, C126S, C126A, C126V, C126M and C126T have been characterized. Crystal structures of 3-phosphoglycolate (PGA) bound C126S mutant and the unliganded forms of the C126S and C126A mutants have been determined at a resolution of 1.7 Å to 2.1 Å. Kinetic studies reveal a ~5 fold drop in kcat for the C126S and C126A mutants, while a ~ 10 fold drop is observed for the other three mutants. All the mutants show reduced stability at lower concentration and higher temperature. Chapter 3 presents the kinetic and structural characterization for the E97Q and E97D mutants of Pf TIM. A 4000 fold reduction in kcat is observed for E97Q, 100 fold reduction for the E97D mutant, while a ~ 9000 fold drop in activity for the control mutant, E165A. A large conformational change for the critical K12 side chain is observed in the crystal structure of the E97Q mutant, while it remains unchanged in the E97D structure. The results are interpreted to invoke a direct role for E97 in the catalytic proton transfer cycle, eliminating the need to invoke the formation of the energetically unfavorable imidazolate anion at H95. Chapter 4 reports investigations with position 96 by the biochemical and structural characterization of single mutants, F96Y, F96A and the double mutants, F96S/S73A and F96S/L167V. F96Y showed ~100 fold drop in activity, F96A revealed ~10 fold drop in activity, while F96S/S73A showed 100 fold lower activity than that of the wild type enzyme. Interestingly, the double mutant F96S/L167V proved to be a partial pseudorevertant, showing 10 fold higher activity than the single mutant, F96S. Chapter 5 describes the cloning, and preliminary kinetic and biophysical characterization of the enzyme, Dm TIM. A survey of disease causing mutations in TIM and the relationship of these sites of mutation to the active site and the dimer interface of TIM is presented in this Chapter.

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Gokhale, Rajesh S. "Protein Engineering Studies Of The Dimeric Enzymes Thymidylate Synthase And Triosephosphate Isomerase." Thesis, 1996. http://etd.iisc.ernet.in/handle/2005/1690.

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Shu-FengYeh and 葉書鋒. "Analysis The Correlation between Triosephosphate Isomerase 1 (TPI1) and Malignancy of Lung Cancer." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/6479yy.

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33

Ravindra, Gudihal. "Studies On Triosephosphate Isomerase From Plasmodium falciparum And Designed Internally Quenched Fluorescent Protease Substrates." Thesis, 2004. http://etd.iisc.ernet.in/handle/2005/1186.

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Li, Wenbo. "Investigation of Slow Dynamics in Proteins: NMR Pulse Sequence Development and Application in Triosephosphate Isomerase." Thesis, 2012. https://doi.org/10.7916/D8QJ7QDS.

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The dynamics of proteins on the millisecond time scale are on the same time scale as typical catalytic turnover rates, and can sometimes be closely related to enzymes' functions. Solid state NMR, equipped with magic angle spinning, is a very good technique to detect such millisecond dynamics, because it is suitable for many protein systems such as membrane proteins, and the anisotropic interactions recoupled in the solid state NMR can supply valuable geometric information regarding the dynamics. In this thesis, I mainly focus on the developing new dynamics detection pulse sequences based on previous Centerband-Only Detection of Exchange (CODEX) experiment and applying CODEX experiments to an enzyme system, triosephosphate isomerase (TIM), for studying the function of the millisecond dynamics in catalysis. Two newly developed pulse sequences, Dipolar CODEX and R-CODEX use the 13C-15N (Dipolar CODEX) and 1H-13C or 1H-15N (R-CODEX) dipolar couplings to detect dynamics. Compared with the chemical shift anisotropy used in the CODEX experiment, the dipolar coupling has a more direct relationship with the molecular geometry and could be better for extracting geometric information regarding reorientations. A special characteristic of the R-CODEX sequence is that the use of an R-type dipolar recoupling sequence can suppress the effect of 1H-1H homonuclear couplings. This approach paves the way to detect both the correlation time and reorientational angle of the dynamics in fully protonated samples. These two pulse sequences are tested by detecting the π flip motion of urea and methylsulfone imidazole. The R-CODEX experiment is compared with two other millisecond dynamics detection methods: 2D-exchange experiments and line-shape analysis, using the example of in crystalline L-phenylalanine hydrochloride. The millisecond ring flip motion of the aromatic ring in L-phenylalanine hydrochloride is characterized in detail for the first time. The comparison between these three methods shows that the R-CODEX experiment does not require a chemical shift change in the process of the motion and that it can detect the dynamics even if there is the peak overlap in the spectra. Triosephosphate isomerase (TIM) is a well-known highly efficient enzyme. Its loop motion (loop 6) has been extensively studied and been proven to be correlated with product release and be a rate-limiting step for the catalysis. Another highly conserved loop near the active site, loop 7 also has large changes in dihedral angles during ligand binding. Its motion is suspected to be correlated with loop 6 based on mutant experiments and solution NMR studies. However, the core sequence of loop 7, YGGS, is missing in the solution NMR spectrum. We assigned the GG pair in loop 7 (G209-G210) using 1-13C, 15N glycine labeling and solid state NMR experiments, and detected the loop 7's motion using 1-13C glycine labeling and CODEX experiments. We found that loop 7's motional rate (300+/-100 s-1) at -10oC agrees well with previously detected motional rates of loop 6 extrapolated from higher temperatures using an Arrhenius plot. This suggeststhat the motion of loop 6 probably correlates with loop 7. At the same time, the line-shape analysis for another GG pair (G232-G233), which forms hydrogen bonds with the ligand, indicates a ligand release rate (400+/-100 s-1) similar to loop 7's rate, supporting the hypothesis that the ligand release is also probably correlated with the motion of loop 7 and loop 6.

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35

Shahul, Hameed M. S. "Structural Studies Of E. Coli Thioredoxin And P. Falciparum Triosephosphate Isomerase By NMR And Computational Methods." Thesis, 2012. http://hdl.handle.net/2005/2315.

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To unravel the mysteries of complex biological processes carried out by biomolecules it is necessary to adopt a multifaceted approach, which involves employing a wide variety of tools both computational and experimental. In order to gain a clear understanding of the function of biomolecules their three dimensional structure is required. X-ray crystallography and Nuclear Magnetic Resonance (NMR) spectroscopy are the only two methods capable of providing high-resolution three-dimensional structure of biomolecules. NMR has the advantage of allowing the study of structure of biomolecules in solution and is better equipped to characterize the dynamics of the protein. Protein structure determination by NMR spectroscopy consists of recombinant expression of isotopically labeled proteins, purification, data collection, data processing, resonance assignment, distance restraint and angular restraint generation, structure calculation and structure validation. Apart from 3D structure determination of biomolecules NMR has become the method of choice for studying transient protein-protein interactions, which are notoriously difficult to study at higher resolution by other methods. Mass spectrometry plays an important role in enabling rapid identification of biomolecules and their modifications. The high sensitivity and resolution mass spectrometry offers makes it the method of choice for studying post-transitional modification of proteins. Use of computers in biology has played an essential role in elucidating those structure function relationships in biomolecules that are not possible to study by experimental techniques. The first chapter of this thesis deals with the introduction of methods used in this study. A brief introduction about the theory of Nuclear Magnetic Resonance (NMR) spectroscopy is given. Protein NMR methods used for structure determination of medium sized proteins are discussed. A part of this chapter discusses about the application of mass spectrometry in biochemistry and the use of tandem MS/MS experiments in identification of proteins and peptide fragments. Finally, the last part of this chapter gives an introduction about the theory of molecular dynamics and techniques used in the post processing of MD trajectories to elucidate the dynamics of proteins. The second chapter of this thesis is concerned with NMR characterization of a novel protein-protein interaction between the glycolytic enzyme Triosephosphate isomerase and the redox protein Thioredoxin. Chemical shift perturbation studies have been done to map the binding interfaces of these proteins. The structure of the complex was then modeled using NMR restraints based docking using the known 3D structure of these proteins. The docked complex reveals crucial insights into the glutathione mediated redox regulation of Triosephosphate isomerase and the role of thioredoxin as a deglutathionylating agent. Enzyme activity assays of Triosephosphate isomerase were done to show the inhibitory effects of s-glutathionylation of Cys217 and the role of thioredoxin as a deglutathionylating agent. The third chapter of the thesis is aimed to address some important issues related to the inhibition of Plasmodium falciparum Triosephosphate isomerase by S-glutathionylation. Oxidative stress induces protein glutathionylation which is a reversible post translational modification consisting of the formation of a mixed disulfide between protein cysteines and glutathione. Mass spectrometric analysis of the kilnetics of glutathionylation along with enzyme activity assays clearly show that gluthionylation of either Cys-13 (situated in the dimmer interface) or Cys-217 (situated in Helix G) can render the enzyme inactive. Molecular dynamics simulations provide a mechanistic basis of inhibition and predict that glutathionylation at Cys217 allosterically induces loop 6 disorder. The fourth chapter of this thesis addresses the stabilizing effect of introduction of a cross-strand disulfide bond across a non-hydrogen bonded position of an antiparallel beta sheet. Multidimensional heteronuclear NMR experiments have been used to get the backbone and side-chain resonance assignments, distance and angular restraints. In addition RDC based restraints have been used to calculate the structure of oxidixed form of L79C, T89C thiroedoxin. The observation of predominantly –RH staple conformation among the NMR ensemble in typical of cross-strand disulfides. The fifth chapter of this thesis deals with the dynamics of thioredoxin using computational methods.In this chapter analysis of known complexes of thiroedoxin was done to determine binding hot spot residues using free energy calculations. The physicochemical basis for the multispecificity of thioredoxin is probed using molecular dynamics simulations. In this chapter it has been shown that conformational selection plays a very important role in thioredoxin target recognition.

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Eaazhisai, K. "Structural Studies By X-ray Diffraction On Two Key Enzymes Of Plasmodium falciparum : Triosephosphate Isomerase And Adenylosuccinate Synthetase." Thesis, 2004. http://etd.iisc.ernet.in/handle/2005/1188.

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37

Sedaghatkish, Afsaneh. "Carbon metabolism in transgenic roots with altered levels of hexokinase and triosephosphate isomerase and growing under different nitrogen status." Thèse, 2013. http://hdl.handle.net/1866/9098.

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Ce projet a pour but d’évaluer la capacité de la voie des pentoses phosphates (VPP) dans les racines transgéniques de pomme de terre (Solanum tuberosum) modifiées pour exprimer différents niveaux de l'hexokinase (HK) et de la triosephosphate isomérase cytosolique (cTPI). Dans les racines, la VPP alimente la voie de l’assimilation de l’azote en equivalents réducteurs et permet donc la biosynthèse des acides aminés. Le glucose-6-phosphate produit par l’HK est consommé par la partie oxydative de la VPP catalysée par la glucose-6-phosphate déshydrogénase (G6PDH) et la 6-phosphogluconate déshydrogénase (6PGDH). Les changements dans l'expression de HK et cTPI peuvent affecter le fonctionnement de la VPP et les mécanismes qui sont liés à l’utilisation des équivalents réducteurs produits par la VPP, comme l'assimilation de l’azote et la synthèse des acides aminés. Afin d’évaluer l’effet des manipulations génétiques de l’HK et de la cTPI sur l’assimilation de l’azote, nous avons cultivé les racines transgéniques sur des milieux contenant des concentrations élevées (7 mM) ou basses (0,7 mM) de nitrate d’ammonium comme source d’azote. Les résultats montrent que la culture sur un milieu riche en azote induit les activités G6PDH et 6PGDH. Les données montrent que la capacité de la VPP est plus grande avec des niveaux élevés en HK ou en cTPI. Nous avons aussi pu démontrer une plus grande activité spécifique de l’HK dans les conditions pauvres en azote. Ces données ont été complémentées par des mesures des pools d’acides aminés dans les racines transgéniques cultivées sur différents niveaux d’azote. Aucune tendance notable des pools d’acides aminés n’a été remarquée dans les racines modifiées pour leur contenu en HK suggèrant que la manipulation de HK n’affecte pas l'assimilation de l’azote. Dans les racines transgéniques modifiées pour la cTPI, les ratios Gln/Glu et Asn/Asp sont plus élevés chez les clones antisens, indiquant une assimilation de l’azote plus élevée. Ces résultats ont démontré l'activation de l'assimilation de l’azote chez les clones antisens cTPI dans les conditions élevées et basses d’azote alors que la manipulation de l’HK n’affecte pas l’assimilation de l’azote.
This study investigates the capacity of the oxidative pentose phosphate pathway (oxPPP) and nitrogen metabolism in transgenic potato (Solanum tuberosum) roots modified to express different levels of hexokinase (HK) or cytosolic triosephosphate isomerase (cTPI) growing under different nitrogen regimes. The flux of carbon through the oxPPP in cTPI antisense roots is higher than control roots growing under high supply of N. On the other hand, the conversion of Glucose (Glc) to Glucose-6-phosphate (G6P) is higher in roots overexpressing HK than in antisense HK roots growing at a high level of N. Therefore, overexpression of HK or down regulation of cTPI activities in transgenic roots might be compensated by increased C catabolism through the oxPPP. In order to see the affect of HK and cTPI manipulation on N assimilation, the transgenic roots were grown on media with low or high concentration of ammonium nitrate as the N source. The specific activity of the oxPPP enzymes glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) were both increased by an increased N supply in HK and cTPI transgenic roots. This is consistent with the provision of reducing equivalents for N assimilation. The data also show that the capacity of the oxPPP is higher in roots with high HK or cTPI activity. We were able to detect higher HK specific activity in N deficient conditions. These data were complemented with measurements of amino acid pools in transgenic roots. No trend in amino acid pools was found in roots modified for HK activity. However, down regulation of cTPI led to higher Gln, Gln/Glu and Asn/Asp ratios, indicating higher assimilation of N. These results demonstrated the activation of N assimilation in cTPI antisense clones while the manipulation of HK is unlikely to affect the N assimilation.

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38

Banerjee, Mousumi. "Structure-Function Studies On Triosephoshate Isomerase From Plasmodium falciparum And Methanocaldococcus jannaschii." Thesis, 2008. http://hdl.handle.net/2005/824.

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This thesis describes studies directed towards understanding structure-function relationships of triosephosphate isomerase (TIM), from a protozoan parasite Plasmodium falciparum and a thermophilic archaea Methanocaldococcus jannaschii. Triosephosphate isomerase, a ubiquitous glycolytic enzyme, has been the subject of biochemical, enzymatic and structural studies for the last five decades. Studies on TIM have been central to the development of mechanistic enzymology. The present study investigates the role of specific residues in the structure and function of Plasmodium falciparum triosephosphate isomerase (PfTIM). The structure and stability of a tetrameric triosephosphate isomerase from Methanocaldococcus jannaschii (MjTIM) is also presented. Chapter 1 provides a general introduction to the glycolytic enzyme triosephosphate isomerase, conservation of TIM sequences, its fold and three dimensional organization. The isomerisation reaction interconverting dihydroxyacetone phosphate and glyceraldehyde 3phosphate catalyzed by triosephosphate isomerase is an example of a highly stereospecific proton transfer process (Hall & Knowles, 1975; Rieder & Rose, 1959). This chapter briefly reviews mechanistic features and discusses the role of active site residues and the functional flexible loop 6. Triosephosphate isomerase adopts the widely occurring ( β/ α)8 barrel fold and mostly occurs as a dimer (Banner et al., 1975). Protein engineering studies, related to folding, stability and design of monomeric TIM are also addressed. A brief introduction to thermophilic TIMs and higher oligomeric TIMs is given. The role of this enzyme in disease states like hemolytic anemia and neuromuscular dysfunction is surveyed. The production of methylglyoxal, a toxic metabolite, as a byproduct of the TIM reaction is also considered. Many proteins utilize segmental motions to catalyze a specific reaction. The omega loop (loop 6) of triosephosphate isomerase is important for preventing the ene-diol intermediate from forming the cytotoxic byproduct, methylglyoxal. The active site loop-6 of triosephosphate isomerase moves about 7Ǻ on ligand binding. It exhibits a hinged lid motion alternating between two well defined, “open” and “closed”, conformations (Joseph et al., 1990). Though the movement of loop 6 is not ligand gated, in crystals the ligand bound forms invariably reveal a closed loop conformation. Plasmodium falciparum TIM is an exception which predominantly exhibits “open” loop conformations, even in the ligand bound state (Parthasarathy et al., 2002). Phe 96 is a key residue that is involved in contacts between the flexible loop-6 and the protein body in PfTIM. Notably, in all TIM sequences determined thus far, with the exception of plasmodial sequences, this residue is Ser 96. In Chapter 2 the mutants F96S, F96H and F96W are reported. The crystal structures of the mutant enzymes with or without bound ligand are described. In all the ligand free cases, loop-6 adopts an “open” conformation. Kinetic parameters for all the mutants establish that residue 96 does not play an essential role in modulating the loop conformation but may be important for ligand binding. Structural analysis of the mutants along with WT enzyme reveals the presence of a water network which can modulate ligand binding. Subunit interfaces of oligomeric proteins provide an opportunity to understand protein- protein interactions. Chapter 3 describes biochemical and biophysical studies on two separate dimer-interface destabilizing mutants C13E and W11F/W168F/Y74W of PfTIM. The intention was to generate a stable monomer by disrupting the interaction hubs. C13 is a part of a large hydrophobic patch (Maithal et al., 2002a) at the dimer interface. Introduction of a negative charge at position 13 destabilizes the interface and reduces activity. Y74 is a part of an aromatic cluster of the interface (Maithal et al., 2002b). The Y74W triple mutant was designed to disrupt the aromatic cluster by introducing additional atoms. Tryptophan is also a fluorophore, allowing studies of the dimer disruption by fluorescence, after mutating the two inherent tryptophan residues, W11 and W168 to phenylalanine. The mutants showed reduced activity and were more sensitive than the wild type enzyme to chemical denaturants as well as thermal denaturation. Evidenced for monomer formation is presented. These studies together with previous work reveal that the interface is important for both activity and stability. In order to develop a model for understanding the relationship between protein stabilization and oligomeric status, characterization of the TIM from Methanocaldococcus jannaschii (MjTIM) has been undertaken. Chapter 4 describes the purification and characterization of MjTIM. The MjTIM gene was cloned and expressed in pTrc99A and protein was isolated from AA200 E. coli cells. Hyperexpressed protein was purified to homogeneity and relevant kinetic parameters have been determined. The tetrameric nature of MjTIM is established by gel filtration studies. Circular dichroism (CD) studies establish the stability of the overall fold, even at temperatures as high as 95ºC. A surprising loss of enzyme activity upon prolonged incubation at high temperature was observed. ESI-MS studies establish that oxidation of thiol groups of the protein may be responsible for the thermal inactivation. Chapter 5 describes the molecular structure of MjTIM, determined in collaboration with Prof. MRN Murthy’s group at the Indian Institute of Science (Gayathri et al., 2007). The crystal structure of the recombinant triosephosphate isomerase (TIM) from the archaeabacteria Methanocaldococcus jannaschii has been determined at a resolution of 2.3 Å. MjTIM is tetrameric, as suggested by solution studies and from the crystal structure, as in the case of two other structurally characterised archaeal TIMs. The archaeabacterial TIMs are shorter compared to the dimeric TIMs, with the insertions in the dimeric TIMs occurring in the vicinity of the putative tetramer interface, resulting in a hindrance to tetramerization in the dimeric TIMs. The charge distribution on the surface of archaeal TIMs also facilitates tetramerization. Analysis of the barrel interactions in TIMs suggests that these interactions are unlikely to account for the thermal stability of archaeal TIMs. A feature of the unliganded structure of MjTIM is the complete absence of electron density for the loop 6 residues. The disorder of the loop may be ascribed to a missing salt bridge between residues at the N- and C- terminal ends of the loop in MjTIM. Chapter 6 is a follow up of an interesting observation made by Vogel and Chmielewski (1994), who noticed that subtilisin cleaved rabbit muscle triosephosphate isomerase religated spontaneously upon addition of organic solvents. Further extension of this nicking and religation process with PfTIM emphasizes the importance of tertiary interactions in contributing to the stability of the (β/α)8 barrel folds (Ray et al., 1999). This chapter establishes that subtilisin nicking and religation is also facile in thermophilic MjTIM. Fragments generated by subtilisin nicking were identified using MALDI mass spectrometry at early and late stages of the cleavage for both the dimeric PfTIM and tetrameric MjTIM. This chapter also describes the comparative thermal and denaturant stability of both the enzymes. The accessibility of the Cys residues of MjTIM has been probed by examining the rates of labeling of thiol groups by iodoacetamide. The differential labeling of Cys residues has been demonstrated by mass spectrometry. Chapter 7 summarizes the main results and conclusions of the studies described in this thesis.

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