Journal articles: 'Outer membrane protein'

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Hazlett, Karsten R. O., David L. Cox, Marc Decaffmeyer, Michael P. Bennett, Daniel C. Desrosiers, Carson J. La Vake, Morgan E. La Vake, et al. "TP0453, a Concealed Outer Membrane Protein of Treponema pallidum, Enhances Membrane Permeability." Journal of Bacteriology 187, no. 18 (September 15, 2005): 6499–508. http://dx.doi.org/10.1128/jb.187.18.6499-6508.2005.

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ABSTRACT The outer membrane of Treponema pallidum, the noncultivable agent of venereal syphilis, contains a paucity of protein(s) which has yet to be definitively identified. In contrast, the outer membranes of gram-negative bacteria contain abundant immunogenic membrane-spanning β-barrel proteins mainly involved in nutrient transport. The absence of orthologs of gram-negative porins and outer membrane nutrient-specific transporters in the T. pallidum genome predicts that nutrient transport across the outer membrane must differ fundamentally in T. pallidum and gram-negative bacteria. Here we describe a T. pallidum outer membrane protein (TP0453) that, in contrast to all integral outer membrane proteins of known structure, lacks extensive β-sheet structure and does not traverse the outer membrane to become surface exposed. TP0453 is a lipoprotein with an amphiphilic polypeptide containing multiple membrane-inserting, amphipathic α-helices. Insertion of the recombinant, nonlipidated protein into artificial membranes results in bilayer destabilization and enhanced permeability. Our findings lead us to hypothesize that TP0453 is a novel type of bacterial outer membrane protein which may render the T. pallidum outer membrane permeable to nutrients while remaining inaccessible to antibody.

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Ishikawa, Daigo, Hayashi Yamamoto, Yasushi Tamura, Kaori Moritoh, and Toshiya Endo. "Two novel proteins in the mitochondrial outer membrane mediate β-barrel protein assembly." Journal of Cell Biology 166, no. 5 (August 23, 2004): 621–27. http://dx.doi.org/10.1083/jcb.200405138.

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Mitochondrial outer and inner membranes contain translocators that achieve protein translocation across and/or insertion into the membranes. Recent evidence has shown that mitochondrial β-barrel protein assembly in the outer membrane requires specific translocator proteins in addition to the components of the general translocator complex in the outer membrane, the TOM40 complex. Here we report two novel mitochondrial outer membrane proteins in yeast, Tom13 and Tom38/Sam35, that mediate assembly of mitochondrial β-barrel proteins, Tom40, and/or porin in the outer membrane. Depletion of Tom13 or Tom38/Sam35 affects assembly pathways of the β-barrel proteins differently, suggesting that they mediate different steps of the complex assembly processes of β-barrel proteins in the outer membrane.

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Mayer, A., R. Lill, and W. Neupert. "Translocation and insertion of precursor proteins into isolated outer membranes of mitochondria." Journal of Cell Biology 121, no. 6 (June 15, 1993): 1233–43. http://dx.doi.org/10.1083/jcb.121.6.1233.

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Nuclear-encoded proteins destined for mitochondria must cross the outer or both outer and inner membranes to reach their final sub-mitochondrial locations. While the inner membrane can translocate preproteins by itself, it is not known whether the outer membrane also contains an endogenous protein translocation activity which can function independently of the inner membrane. To selectively study the protein transport into and across the outer membrane of Neurospora crassa mitochondria, outer membrane vesicles were isolated which were sealed, in a right-side-out orientation, and virtually free of inner membranes. The vesicles were functional in the insertion and assembly of various outer membrane proteins such as porin, MOM19, and MOM22. Like with intact mitochondria, import into isolated outer membranes was dependent on protease-sensitive surface receptors and led to correct folding and membrane integration. The vesicles were also capable of importing a peripheral component of the inner membrane, cytochrome c heme lyase (CCHL), in a receptor-dependent fashion. Thus, the protein translocation machinery of the outer mitochondrial membrane can function as an independent entity which recognizes, inserts, and translocates mitochondrial preproteins of the outer membrane and the intermembrane space. In contrast, proteins which have to be translocated into or across the inner membrane were only specifically bound to the vesicles, but not imported. This suggests that transport of such proteins involves the participation of components of the intermembrane space and/or the inner membrane, and that in these cases the outer membrane translocation machinery has to act in concert with that of the inner membrane.

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Dhar, Rik, and Joanna SG Slusky. "Outer membrane protein evolution." Current Opinion in Structural Biology 68 (June 2021): 122–28. http://dx.doi.org/10.1016/j.sbi.2021.01.002.

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Slusky, Joanna SG. "Outer membrane protein design." Current Opinion in Structural Biology 45 (August 2017): 45–52. http://dx.doi.org/10.1016/j.sbi.2016.11.003.

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Murcha, Monika W., Dina Elhafez, A. Harvey Millar, and James Whelan. "The C-terminal Region of TIM17 Links the Outer and Inner Mitochondrial Membranes inArabidopsisand Is Essential for Protein Import." Journal of Biological Chemistry 280, no. 16 (February 18, 2005): 16476–83. http://dx.doi.org/10.1074/jbc.m413299200.

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The translocase of the inner membrane 17 (AtTIM17-2) protein fromArabidopsishas been shown to link the outer and inner mitochondrial membranes. This was demonstrated by several approaches: (i)In vitroorganelle import assays indicated the importedAtTIM17-2 protein remained protease accessible in the outer membrane when inserted into the inner membrane. (ii) N-terminal and C-terminal tagging indicated that it was the C-terminal region that was located in the outer membrane. (iii) Antibodies raised to the C-terminal 100 amino acids recognize a 31-kDa protein from purified mitochondria, but cross-reactivity was abolished when mitochondria were protease-treated to remove outer membrane-exposed proteins. Antibodies toAtTIM17-2 inhibited import of proteins via the general import pathway into outer membrane-ruptured mitochondria, but did not inhibit protein import via the carrier import pathway. Together these results indicate that the C-terminal region ofAtTIM17-2 is exposed on the outer surface of the outer membrane, and the C-terminal region is essential for protein import into mitochondria.

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Hoffmann, Juliane J., and Thomas Becker. "Crosstalk between Mitochondrial Protein Import and Lipids." International Journal of Molecular Sciences 23, no. 9 (May 9, 2022): 5274. http://dx.doi.org/10.3390/ijms23095274.

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Mitochondria import about 1000 precursor proteins from the cytosol. The translocase of the outer membrane (TOM complex) forms the major entry site for precursor proteins. Subsequently, membrane-bound protein translocases sort the precursor proteins into the outer and inner membrane, the intermembrane space, and the matrix. The phospholipid composition of mitochondrial membranes is critical for protein import. Structural and biochemical data revealed that phospholipids affect the stability and activity of mitochondrial protein translocases. Integration of proteins into the target membrane involves rearrangement of phospholipids and distortion of the lipid bilayer. Phospholipids are present in the interface between subunits of protein translocases and affect the dynamic coupling of partner proteins. Phospholipids are required for full activity of the respiratory chain to generate membrane potential, which in turn drives protein import across and into the inner membrane. Finally, outer membrane protein translocases are closely linked to organellar contact sites that mediate lipid trafficking. Altogether, intensive crosstalk between mitochondrial protein import and lipid biogenesis controls mitochondrial biogenesis.

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Court, Deborah A., Roland Lill, and Walter Neupert. "The protein import apparatus of the mitochondrial outer membrane." Canadian Journal of Botany 73, S1 (December 31, 1995): 193–97. http://dx.doi.org/10.1139/b95-245.

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The majority of proteins within mitochondria are synthesized on cytosolic ribosomes and imported into the organelles. Protein complexes in the mitochondrial outer membrane harbour both the receptors that recognize these preproteins, and a translocation pore. These "receptor complexes" are the entry points for most preproteins, which are subsequently targeted to their final submitochondrial locations. The outer membrane complexes cooperate with the import machinery of the inner membrane to target preproteins to the inner membrane itself, the matrix, or, in some cases, to the intermembrane space. In isolated outer membranes, these complexes are capable of accurately importing preproteins destined for the outer membrane. Our current understanding of the composition, function, and biogenesis of these outer membrane receptor complexes is the focus of this article. Key words: mitochondria, outer membrane, protein import, receptors.

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Pon, L., T. Moll, D. Vestweber, B. Marshallsay, and G. Schatz. "Protein import into mitochondria: ATP-dependent protein translocation activity in a submitochondrial fraction enriched in membrane contact sites and specific proteins." Journal of Cell Biology 109, no. 6 (December 1, 1989): 2603–16. http://dx.doi.org/10.1083/jcb.109.6.2603.

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To identify the membrane regions through which yeast mitochondria import proteins from the cytoplasm, we have tagged these regions with two different partly translocated precursor proteins. One of these was bound to the mitochondrial surface of ATP-depleted mitochondria and could subsequently be chased into mitochondria upon addition of ATP. The other intermediate was irreversibly stuck across both mitochondrial membranes at protein import sites. Upon subfraction of the mitochondria, both intermediates cofractionated with membrane vesicles whose buoyant density was between that of inner and outer membranes. When these vesicles were prepared from mitochondria containing the chaseable intermediate, they internalized it upon addition of ATP. A non-hydrolyzable ATP analogue was inactive. This vesicle fraction contained closed, right-side-out inner membrane vesicles attached to leaky outer membrane vesicles. The vesicles contained the mitochondrial binding sites for cytoplasmic ribosomes and contained several mitochondrial proteins that were enriched relative to markers of inner or outer membranes. By immunoelectron microscopy, two of these proteins were concentrated at sites where mitochondrial inner and outer membranes are closely apposed. We conclude that these vesicles contain contact sites between the two mitochondrial membranes, that these sites are the entry point for proteins into mitochondria, and that the isolated vesicles are still translocation competent.

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Braun, Volkmar. "The Outer Membrane Took Center Stage." Annual Review of Microbiology 72, no. 1 (September 8, 2018): 1–24. http://dx.doi.org/10.1146/annurev-micro-090817-062156.

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My interest in membranes was piqued during a lecture series given by one of the founders of molecular biology, Max Delbrück, at Caltech, where I spent a postdoctoral year to learn more about protein chemistry. That general interest was further refined to my ultimate research focal point—the outer membrane of Escherichia coli—through the influence of the work of Wolfhard Weidel, who discovered the murein (peptidoglycan) layer and biochemically characterized the first phage receptors of this bacterium. The discovery of lipoprotein bound to murein was completely unexpected and demonstrated that the protein composition of the outer membrane and the structure and function of proteins could be unraveled at a time when nothing was known about outer membrane proteins. The research of my laboratory over the years covered energy-dependent import of proteinaceous toxins and iron chelates across the outer membrane, which does not contain an energy source, and gene regulation by iron, including transmembrane transcriptional regulation.

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Grevel, Alexander, and Thomas Becker. "Porins as helpers in mitochondrial protein translocation." Biological Chemistry 401, no. 6-7 (May 26, 2020): 699–708. http://dx.doi.org/10.1515/hsz-2019-0438.

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AbstractMitochondria import the vast majority of their proteins via dedicated protein machineries. The translocase of the outer membrane (TOM complex) forms the main entry site for precursor proteins that are produced on cytosolic ribosomes. Subsequently, different protein sorting machineries transfer the incoming preproteins to the mitochondrial outer and inner membranes, the intermembrane space, and the matrix. In this review, we highlight the recently discovered role of porin, also termed voltage-dependent anion channel (VDAC), in mitochondrial protein biogenesis. Porin forms the major channel for metabolites and ions in the outer membrane of mitochondria. Two different functions of porin in protein translocation have been reported. First, it controls the formation of the TOM complex by modulating the integration of the central receptor Tom22 into the mature translocase. Second, porin promotes the transport of carrier proteins toward the carrier translocase (TIM22 complex), which inserts these preproteins into the inner membrane. Therefore, porin acts as a coupling factor to spatially coordinate outer and inner membrane transport steps. Thus, porin links metabolite transport to protein import, which are both essential for mitochondrial function and biogenesis.

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Ryan, Kathleen R., James A. Taylor, and Lisa M. Bowers. "The BAM complex subunit BamE (SmpA) is required for membrane integrity, stalk growth and normal levels of outer membrane β-barrel proteins in Caulobacter crescentus." Microbiology 156, no. 3 (March 1, 2010): 742–56. http://dx.doi.org/10.1099/mic.0.035055-0.

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The outer membrane of Gram-negative bacteria is an essential compartment containing a specific complement of lipids and proteins that constitute a protective, selective permeability barrier. Outer membrane β-barrel proteins are assembled into the membrane by the essential hetero-oligomeric BAM complex, which contains the lipoprotein BamE. We have identified a homologue of BamE, encoded by CC1365, which is located in the outer membrane of the stalked alpha-proteobacterium Caulobacter crescentus. BamE associates with proteins whose homologues in other bacteria are known to participate in outer membrane protein assembly: BamA (CC1915), BamB (CC1653) and BamD (CC1984). Caulobacter cells lacking BamE grow slowly in rich medium and are hypersensitive to anionic detergents, some antibiotics and heat exposure, which suggest that the membrane integrity of the mutant is compromised. Membranes of the ΔbamE mutant have normal amounts of the outer membrane protein RsaF, a TolC homologue, but are deficient in CpaC*, an aggregated form of the outer membrane secretin for type IV pili. ΔbamE membranes also contain greatly reduced amounts of three TonB-dependent receptors that are abundant in wild-type cells. Cells lacking BamE have short stalks and are delayed in stalk outgrowth during the cell cycle. Based on these findings, we propose that Caulobacter BamE participates in the assembly of outer membrane β-barrel proteins, including one or more substrates required for the initiation of stalk biogenesis.

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Li, Jian-Ming, and Gordon C. Shore. "Protein sorting between mitochondrial outer and inner membranes. Insertion of an outer membrane protein into the inner membrane." Biochimica et Biophysica Acta (BBA) - Biomembranes 1106, no. 2 (May 1992): 233–41. http://dx.doi.org/10.1016/0005-2736(92)90001-3.

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Ghazaei, Ciamak. "Leptospiral major outer membrane protein." Reviews in Medical Microbiology 26, no. 2 (April 2015): 65–69. http://dx.doi.org/10.1097/mrm.0000000000000022.

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Zahedi, Rene P., Albert Sickmann, Andreas M. Boehm, Christiane Winkler, Nicole Zufall, Birgit Schönfisch, Bernard Guiard, Nikolaus Pfanner, and Chris Meisinger. "Proteomic Analysis of the Yeast Mitochondrial Outer Membrane Reveals Accumulation of a Subclass of Preproteins." Molecular Biology of the Cell 17, no. 3 (March 2006): 1436–50. http://dx.doi.org/10.1091/mbc.e05-08-0740.

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Mitochondria consist of four compartments–outer membrane, intermembrane space, inner membrane, and matrix—with crucial but distinct functions for numerous cellular processes. A comprehensive characterization of the proteome of an individual mitochondrial compartment has not been reported so far. We used a eukaryotic model organism, the yeast Saccharomyces cerevisiae, to determine the proteome of highly purified mitochondrial outer membranes. We obtained a coverage of ∼85% based on the known outer membrane proteins. The proteome represents a rich source for the analysis of new functions of the outer membrane, including the yeast homologue (Hfd1/Ymr110c) of the human protein causing Sjögren–Larsson syndrome. Surprisingly, a subclass of proteins known to reside in internal mitochondrial compartments were found in the outer membrane proteome. These seemingly mislocalized proteins included most top scorers of a recent genome-wide analysis for mRNAs that were targeted to mitochondria and coded for proteins of prokaryotic origin. Together with the enrichment of the precursor form of a matrix protein in the outer membrane, we conclude that the mitochondrial outer membrane not only contains resident proteins but also accumulates a conserved subclass of preproteins destined for internal mitochondrial compartments.

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Hoppins, Suzanne, Jennifer Horner, Cheng Song, J. Michael McCaffery, and Jodi Nunnari. "Mitochondrial outer and inner membrane fusion requires a modified carrier protein." Journal of Cell Biology 184, no. 4 (February 23, 2009): 569–81. http://dx.doi.org/10.1083/jcb.200809099.

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In yeast, three proteins are essential for mitochondrial fusion. Fzo1 and Mgm1 are conserved guanosine triphosphatases that reside in the outer and inner membranes, respectively. At each membrane, these conserved proteins are required for the distinct steps of membrane tethering and lipid mixing. The third essential component is Ugo1, an outer membrane protein in the mitochondrial transport protein family. We show that Ugo1 is a modified member of this family, containing three transmembrane domains and existing as a dimer, a structure that is critical for the fusion function of Ugo1. Our functional analysis of Ugo1 indicates that it is required distinctly for both outer and inner membrane fusion after membrane tethering, indicating that it operates at the lipid-mixing step of fusion. This role is distinct from the fusion dynamin-related proteins and thus demonstrates that at each membrane, a single fusion protein is not sufficient to drive the lipid-mixing step, but instead, this step requires a more complex assembly of proteins.

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Scott, S. V., and S. M. Theg. "A new chloroplast protein import intermediate reveals distinct translocation machineries in the two envelope membranes: energetics and mechanistic implications." Journal of Cell Biology 132, no. 1 (January 1, 1996): 63–75. http://dx.doi.org/10.1083/jcb.132.1.63.

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Chloroplast protein import presents a complex membrane traversal problem: precursor proteins must cross two envelope membranes to reach the stromal compartment. This work characterizes a new chloroplast protein import intermediate which has completely traversed the outer envelope membrane but has not yet reached the stroma. The existence of this intermediate demonstrates that distinct protein transport machineries are present in both envelope membranes, and that they are able to operate independently of one another under certain conditions. Energetic characterization of this pathway led to the identification of three independent energy-requiring steps: binding of the precursor to the outer envelope membrane, outer membrane transport, and inner membrane transport. Localization of the sites of energy utilization for each of these steps, as well as their respective nucleotide specificities, suggest that three different ATPases mediate chloroplast envelope transport.

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Bohnert, Maria, Lena-Sophie Wenz, Ralf M. Zerbes, Susanne E. Horvath, David A. Stroud, Karina von der Malsburg, Judith M. Müller, et al. "Role of mitochondrial inner membrane organizing system in protein biogenesis of the mitochondrial outer membrane." Molecular Biology of the Cell 23, no. 20 (October 15, 2012): 3948–56. http://dx.doi.org/10.1091/mbc.e12-04-0295.

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Mitochondria contain two membranes, the outer membrane and the inner membrane with folded cristae. The mitochondrial inner membrane organizing system (MINOS) is a large protein complex required for maintaining inner membrane architecture. MINOS interacts with both preprotein transport machineries of the outer membrane, the translocase of the outer membrane (TOM) and the sorting and assembly machinery (SAM). It is unknown, however, whether MINOS plays a role in the biogenesis of outer membrane proteins. We have dissected the interaction of MINOS with TOM and SAM and report that MINOS binds to both translocases independently. MINOS binds to the SAM complex via the conserved polypeptide transport–associated domain of Sam50. Mitochondria lacking mitofilin, the large core subunit of MINOS, are impaired in the biogenesis of β-barrel proteins of the outer membrane, whereas mutant mitochondria lacking any of the other five MINOS subunits import β-barrel proteins in a manner similar to wild-type mitochondria. We show that mitofilin is required at an early stage of β-barrel biogenesis that includes the initial translocation through the TOM complex. We conclude that MINOS interacts with TOM and SAM independently and that the core subunit mitofilin is involved in biogenesis of outer membrane β-barrel proteins.

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Tommassen, Jan. "Assembly of outer-membrane proteins in bacteria and mitochondria." Microbiology 156, no. 9 (September 1, 2010): 2587–96. http://dx.doi.org/10.1099/mic.0.042689-0.

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The cell envelope of Gram-negative bacteria consists of two membranes separated by the periplasm. In contrast with most integral membrane proteins, which span the membrane in the form of hydrophobic α-helices, integral outer-membrane proteins (OMPs) form β-barrels. Similar β-barrel proteins are found in the outer membranes of mitochondria and chloroplasts, probably reflecting the endosymbiont origin of these eukaryotic cell organelles. How these β-barrel proteins are assembled into the outer membrane has remained enigmatic for a long time. In recent years, much progress has been reached in this field by the identification of the components of the OMP assembly machinery. The central component of this machinery, called Omp85 or BamA, is an essential and highly conserved bacterial protein that recognizes a signature sequence at the C terminus of its substrate OMPs. A homologue of this protein is also found in mitochondria, where it is required for the assembly of β-barrel proteins into the outer membrane as well. Although accessory components of the machineries are different between bacteria and mitochondria, a mitochondrial β-barrel OMP can be assembled into the bacterial outer membrane and, vice versa, bacterial OMPs expressed in yeast are assembled into the mitochondrial outer membrane. These observations indicate that the basic mechanism of OMP assembly is evolutionarily highly conserved.

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Rassow, J., B. Guiard, U. Wienhues, V. Herzog, F. U. Hartl, and W. Neupert. "Translocation arrest by reversible folding of a precursor protein imported into mitochondria. A means to quantitate translocation contact sites." Journal of Cell Biology 109, no. 4 (October 1, 1989): 1421–28. http://dx.doi.org/10.1083/jcb.109.4.1421.

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Passage of precursor proteins through translocation contact sites of mitochondria was investigated by studying the import of a fusion protein consisting of the NH2-terminal 167 amino acids of yeast cytochrome b2 precursor and the complete mouse dihydrofolate reductase. Isolated mitochondria of Neurospora crassa readily imported the fusion protein. In the presence of methotrexate import was halted and a stable intermediate spanning both mitochondrial membranes at translocation contact sites accumulated. The complete dihydrofolate reductase moiety in this intermediate was external to the outer membrane, and the 136 amino acid residues of the cytochrome b2 moiety remaining after cleavage by the matrix processing peptidase spanned both outer and inner membranes. Removal of methotrexate led to import of the intermediate retained at the contact site into the matrix. Thus unfolding at the surface of the outer mitochondrial membrane is a prerequisite for passage through translocation contact sites. The membrane-spanning intermediate was used to estimate the number of translocation sites. Saturation was reached at 70 pmol intermediate per milligram of mitochondrial protein. This amount of translocation intermediates was calculated to occupy approximately 1% of the total surface of the outer membrane. The morphometrically determined area of close contact between outer and inner membranes corresponded to approximately 7% of the total outer membrane surface. Accumulation of the intermediate inhibited the import of other precursor proteins suggesting that different precursor proteins are using common translocation contact sites. We conclude that the machinery for protein translocation into mitochondria is present at contact sites in limited number.

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Becker, Thomas, Lena-Sophie Wenz, Vivien Krüger, Waltraut Lehmann, Judith M. Müller, Luise Goroncy, Nicole Zufall, et al. "The mitochondrial import protein Mim1 promotes biogenesis of multispanning outer membrane proteins." Journal of Cell Biology 194, no. 3 (August 8, 2011): 387–95. http://dx.doi.org/10.1083/jcb.201102044.

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The mitochondrial outer membrane contains translocase complexes for the import of precursor proteins. The translocase of the outer membrane complex functions as a general preprotein entry gate, whereas the sorting and assembly machinery complex mediates membrane insertion of β-barrel proteins of the outer membrane. Several α-helical outer membrane proteins are known to carry multiple transmembrane segments; however, only limited information is available on the biogenesis of these proteins. We report that mitochondria lacking the mitochondrial import protein 1 (Mim1) are impaired in the biogenesis of multispanning outer membrane proteins, whereas overexpression of Mim1 stimulates their import. The Mim1 complex cooperates with the receptor Tom70 in binding of precursor proteins and promotes their insertion and assembly into the outer membrane. We conclude that the Mim1 complex plays a central role in the import of α-helical outer membrane proteins with multiple transmembrane segments.

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Botos, Istvan, Nicholas Noinaj, and Susan K. Buchanan. "Insertion of proteins and lipopolysaccharide into the bacterial outer membrane." Philosophical Transactions of the Royal Society B: Biological Sciences 372, no. 1726 (June 19, 2017): 20160224. http://dx.doi.org/10.1098/rstb.2016.0224.

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The bacterial outer membrane contains phospholipids in the inner leaflet and lipopolysaccharide (LPS) in the outer leaflet. Both proteins and LPS must be frequently inserted into the outer membrane to preserve its integrity. The protein complex that inserts LPS into the outer membrane is called LptDE, and consists of an integral membrane protein, LptD, with a separate globular lipoprotein, LptE, inserted in the barrel lumen. The protein complex that inserts newly synthesized outer-membrane proteins (OMPs) into the outer membrane is called the BAM complex, and consists of an integral membrane protein, BamA, plus four lipoproteins, BamB, C, D and E. Recent structural and functional analyses illustrate how these two complexes insert their substrates into the outer membrane by distorting the membrane component (BamA or LptD) to directly access the lipid bilayer. This article is part of the themed issue ‘Membrane pores: from structure and assembly, to medicine and technology’.

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Hwang, S., T. Jascur, D. Vestweber, L. Pon, and G. Schatz. "Disrupted yeast mitochondria can import precursor proteins directly through their inner membrane." Journal of Cell Biology 109, no. 2 (August 1, 1989): 487–93. http://dx.doi.org/10.1083/jcb.109.2.487.

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Import of precursor proteins into the yeast mitochondrial matrix can occur directly across the inner membrane. First, disruption of the outer membrane restores protein import to mitochondria whose normal import sites have been blocked by an antibody against the outer membrane or by a chimeric, incompletely translocated precursor protein. Second, a potential- and ATP-dependent import of authentic or artificial precursor proteins is observed with purified inner membrane vesicles virtually free of outer membrane components. Third, import into purified inner membrane vesicles is insensitive to antibody against the outer membrane. Thus, while outer membrane components are clearly required in vivo, the inner membrane contains a complete protein translocation system that can operate by itself if the outer membrane barrier is removed.

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Jin, Jong Sook, Sang-Oh Kwon, Dong Chan Moon, Mamata Gurung, Jung Hwa Lee, Seung Il Kim, and Je Chul Lee. "Acinetobacter baumannii Secretes Cytotoxic Outer Membrane Protein A via Outer Membrane Vesicles." PLoS ONE 6, no. 2 (February 28, 2011): e17027. http://dx.doi.org/10.1371/journal.pone.0017027.

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Tanzer, Regina J., and Thomas P. Hatch. "Characterization of Outer Membrane Proteins in Chlamydia trachomatis LGV Serovar L2." Journal of Bacteriology 183, no. 8 (April 15, 2001): 2686–90. http://dx.doi.org/10.1128/jb.183.8.2686-2690.2001.

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ABSTRACT We used a photoactivatable, lipophilic reagent, 3′-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine, to label proteins in the outer membrane of elementary bodies ofChlamydia trachomatis LGV serovar L2 and mass spectrometry to identify the labeled proteins. The identified proteins were polymorphic outer membrane proteins E, G, and H, which were made late in the developmental cycle, the major outer membrane protein, and a mixture of 46-kDa proteins consisting of the open reading frame 623 protein and possibly a modified form of the major outer membrane protein.

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Lindén, M., B. D. Nelson, and J. F. Leterrier. "The specific binding of the microtubule-associated protein 2 (MAP2) to the outer membrane of rat brain mitochondria." Biochemical Journal 261, no. 1 (July 1, 1989): 167–73. http://dx.doi.org/10.1042/bj2610167.

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Purified mitochondria from rat brain contain microtubule-associated proteins (MAPs) bound to the outer membrane. Studies of binding in vitro performed with microtubules and with purified microtubule proteins showed that mitochondria preferentially interact with the high-molecular-mass MAPs (and not with Tau protein). Incubation of intact mitochondria with Taxol-stabilized microtubules resulted in the selective trapping of both MAPs 1 and 2 on mitochondria, indicating that an interaction between the two organelles occurred through a site on the arm-like projection of MAPs. Two MAP-binding sites were located on intact mitochondria. The lower-affinity MAP2-binding site (Kd = 2 x 10(-7) M) was preserved and enriched in the outer-membrane fraction, whereas the higher-affinity site (Kd = 1 x 10(-9) M) was destroyed after removing the outer membrane with digitonin. Detergent fractionation of mitochondrial outer membranes saturated with MAP2 bound in vitro showed that MAPs are associated with membrane fragments which contain the pore-forming protein (porin). MAP2 also partially prevents the solubilization of porin from outer membrane, indicating a MAP-induced change in the membrane environment of porin. These observations demonstrate the presence of specific MAP-binding sites on the outer membrane, suggesting an association between porin and the membrane domain involved in the cross-linkage between microtubules and mitochondria.

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Krumpe, Katrin, Idan Frumkin, Yonatan Herzig, Nitzan Rimon, Cagakan Özbalci, Britta Brügger, Doron Rapaport, and Maya Schuldiner. "Ergosterol content specifies targeting of tail-anchored proteins to mitochondrial outer membranes." Molecular Biology of the Cell 23, no. 20 (October 15, 2012): 3927–35. http://dx.doi.org/10.1091/mbc.e11-12-0994.

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Tail-anchored (TA) proteins have a single C-terminal transmembrane domain, making their biogenesis dependent on posttranslational translocation. Despite their importance, no dedicated insertion machinery has been uncovered for mitochondrial outer membrane (MOM) TA proteins. To decipher the molecular mechanisms guiding MOM TA protein insertion, we performed two independent systematic microscopic screens in which we visualized the localization of model MOM TA proteins on the background of mutants in all yeast genes. We could find no mutant in which insertion was completely blocked. However, both screens demonstrated that MOM TA proteins were partially localized to the endoplasmic reticulum (ER) in ∆spf1 cells. Spf1, an ER ATPase with unknown function, is the first protein shown to affect MOM TA protein insertion. We found that ER membranes in ∆spf1 cells become similar in their ergosterol content to mitochondrial membranes. Indeed, when we visualized MOM TA protein distribution in yeast strains with reduced ergosterol content, they phenocopied the loss of Spf1. We therefore suggest that the inherent differences in membrane composition between organelle membranes are sufficient to determine membrane integration specificity in a eukaryotic cell.

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Gruss, Fabian, Franziska Zaehringer, Roman Jakob, Björn Burmann, Sebastian Hiller, and Timm Maier. "A lateral gate for autotransporter and outer membrane protein assembly." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C1492. http://dx.doi.org/10.1107/s2053273314085076.

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β-barrel proteins are key functional components of the outer membranes of gram-negative bacteria, mitochondria and plastids. They mediate transport across the membrane, act as receptors and are involved in bacterial pathogenicity. Despite their crucial roles, assembly and membrane insertion of β-barrel outer membrane proteins, which are mediated by β-barrel membrane proteins of the OMP85 family, have remained elusive. The crystal structure of the Escherichia coli OMP85 protein TamA [1], which is involved in autotransporter biogenesis, now provides a novel perspective on β-barrel membrane protein assembly. The protein was crystallized in lipidic phase and microseeding was employed to obtain high-quality 2.3 Å diffraction data. TamA comprises a 16-stranded transmembrane β-barrel and three N-terminal POTRA domains. The barrel is closed at the extracellular face by a conserved lid loop tightly interacting with a conserved lock region on the inner barrel wall. The C-terminal β-strand of the barrel forms an unusual inward kink, which creates a gate for substrate access to the lipid bilayer and weakens lateral inter-strand connection. These structural features immediately suggest a mechanism of autotransporter insertion based on barrel expansion and lateral release. Based on structural conservation of all core elements [2], this mechanism might well be relevant for the entire OMP85 family.

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Chen, K., X. Chen, and D. J. Schnell. "Mechanism of protein import across the chloroplast envelope." Biochemical Society Transactions 28, no. 4 (August 1, 2000): 485–91. http://dx.doi.org/10.1042/bst0280485.

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The development and maintenance of chloroplasts relies on the contribution of protein subunits from both plastid and nuclear genomes. Most chloroplast proteins are encoded by nuclear genes and are post-translationally imported into the organelle across the double membrane of the chloroplast envelope. Protein import into the chloroplast consists of two essential elements: the specific recognition of the targeting signals (transit sequences) of cytoplasmic preproteins by receptors at the outer envelope membrane and the subsequent translocation of preproteins simultaneously across the double membrane of the envelope. These processes are mediated via the co-ordinate action of protein translocon complexes in the outer (Toe apparatus) and inner (Tic apparatus) envelope membranes.

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Li, Kewei, Wenpeng Gu, Junrong Liang, Yuchun Xiao, Haiyan Qiu, Haoshu Yang, Xin Wang, and Huaiqi Jing. "Gene polymorphism analysis of Yersinia enterocolitica outer membrane protein A and putative outer membrane protein A family protein." BMC Genomics 15, no. 1 (2014): 201. http://dx.doi.org/10.1186/1471-2164-15-201.

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Newstead, Simon, Jeanette Hobbs, Davina Jordan, Elisabeth P. Carpenter, and So Iwata. "Insights into outer membrane protein crystallization." Molecular Membrane Biology 25, no. 8 (January 2008): 631–38. http://dx.doi.org/10.1080/09687680802526574.

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32

Poolman, J. T., and H. Abdillahi. "Outer membrane protein serosubtyping ofNeisseria meningitidis." European Journal of Clinical Microbiology & Infectious Diseases 7, no. 2 (April 1988): 291–92. http://dx.doi.org/10.1007/bf01963104.

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Goose, Joseph, and Mark S. P. Sansom. "Outer Membrane Protein Dynamics in E.coli." Biophysical Journal 100, no. 3 (February 2011): 631a. http://dx.doi.org/10.1016/j.bpj.2010.12.3627.

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Huyer, M., T. R. Parr, R. E. W. Hancock, and W. J. Page. "Outer membrane porin protein ofCampylobacter jejuni." FEMS Microbiology Letters 37, no. 3 (December 1986): 247–50. http://dx.doi.org/10.1111/j.1574-6968.1986.tb01803.x.

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Lopez, Job E., William F. Siems, Guy H. Palmer, Kelly A. Brayton, Travis C. McGuire, Junzo Norimine, and Wendy C. Brown. "Identification of Novel Antigenic Proteins in a Complex Anaplasma marginale Outer Membrane Immunogen by Mass Spectrometry and Genomic Mapping." Infection and Immunity 73, no. 12 (December 2005): 8109–18. http://dx.doi.org/10.1128/iai.73.12.8109-8118.2005.

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ABSTRACT Immunization with purified Anaplasma marginale outer membranes induces complete protection against infection that is associated with CD4+ T-lymphocyte-mediated gamma interferon secretion and immunoglobulin G2 (IgG2) antibody titers. However, knowledge of the composition of the outer membrane immunogen is limited. Recent sequencing and annotation of the A. marginale genome predicts at least 62 outer membrane proteins (OMP), enabling a proteomic and genomic approach for identification of novel OMP by use of IgG serum antibody from outer membrane vaccinates. Outer membrane proteins were separated by two-dimensional electrophoresis, and proteins recognized by total IgG and IgG2 in immune sera of outer membrane-vaccinated cattle were detected by immunoblotting. Immunoreactive protein spots were excised and subjected to liquid chromatography-tandem mass spectrometry. A database search of the A. marginale genome identified 24 antigenic proteins that were predicted to be outer membrane, inner membrane, or membrane-associated proteins. These included the previously characterized surface-exposed outer membrane proteins MSP2, operon associated gene 2 (OpAG2), MSP3, and MSP5 as well as recently identified appendage-associated proteins. Among the 21 newly described antigenic proteins, 14 are annotated in the A. marginale genome and include type IV secretion system proteins, elongation factor Tu, and members of the MSP2 superfamily. The identification of these novel antigenic proteins markedly expands current understanding of the composition of the protective immunogen and provides new candidates for vaccine development.

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Rollauer, Sarah E., Moloud A. Sooreshjani, Nicholas Noinaj, and Susan K. Buchanan. "Outer membrane protein biogenesis in Gram-negative bacteria." Philosophical Transactions of the Royal Society B: Biological Sciences 370, no. 1679 (October 5, 2015): 20150023. http://dx.doi.org/10.1098/rstb.2015.0023.

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Gram-negative bacteria contain a double membrane which serves for both protection and for providing nutrients for viability. The outermost of these membranes is called the outer membrane (OM), and it contains a host of fully integrated membrane proteins which serve essential functions for the cell, including nutrient uptake, cell adhesion, cell signalling and waste export. For pathogenic strains, many of these outer membrane proteins (OMPs) also serve as virulence factors for nutrient scavenging and evasion of host defence mechanisms. OMPs are unique membrane proteins in that they have a β-barrel fold and can range in size from 8 to 26 strands, yet can still serve many different functions for the cell. Despite their essential roles in cell survival and virulence, the exact mechanism for the biogenesis of these OMPs into the OM has remained largely unknown. However, the past decade has witnessed significant progress towards unravelling the pathways and mechanisms necessary for moulding a nascent polypeptide into a functional OMP within the OM. Here, we will review some of these recent discoveries that have advanced our understanding of the biogenesis of OMPs in Gram-negative bacteria, starting with synthesis in the cytoplasm to folding and insertion into the OM.

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Fischer, Wolfgang, Renate Buhrdorf, Elke Gerland, and Rainer Haas. "Outer Membrane Targeting of Passenger Proteins by the Vacuolating Cytotoxin Autotransporter of Helicobacter pylori." Infection and Immunity 69, no. 11 (November 1, 2001): 6769–75. http://dx.doi.org/10.1128/iai.69.11.6769-6775.2001.

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ABSTRACT Helicobacter pylori produces a number of proteins associated with the outer membrane, including adhesins and the vacuolating cytotoxin. These proteins are supposed to integrate into the outer membrane by β-barrel structures, characteristic of the family of autotransporter proteins. By using the SOMPES (shuttle vector-based outer membrane protein expression) system for outer membrane protein production, we were able to functionally express inH. pylori the cholera toxin B subunit genetically fused to the C-terminal VacA domain. We demonstrate that the fusion protein is translocated to the H. pylori outer membrane and that the CtxB domain is exposed on the H. pylori surface. Thus, we provide the first experimental evidence that the C-terminal β-domain of VacA can transport a foreign passenger protein to theH. pylori surface and hence acts as a functional autotransporter.

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Shang, Ellen S., Jonathan T. Skare, Maurice M. Exner, David R. Blanco, Bruce L. Kagan, James N. Miller, and Michael A. Lovett. "Isolation and Characterization of the Outer Membrane ofBorrelia hermsii." Infection and Immunity 66, no. 3 (March 1, 1998): 1082–91. http://dx.doi.org/10.1128/iai.66.3.1082-1091.1998.

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ABSTRACT The outer membrane of Borrelia hermsii has been shown by freeze-fracture analysis to contain a low density of membrane-spanning outer membrane proteins which have not yet been isolated or identified. In this study, we report the purification of outer membrane vesicles (OMV) from B. hermsii HS-1 and the subsequent identification of their constituent outer membrane proteins. The B. hermsii outer membranes were released by vigorous vortexing of whole organisms in low-pH, hypotonic citrate buffer and isolated by isopycnic sucrose gradient centrifugation. The isolated OMV exhibited porin activities ranging from 0.2 to 7.2 nS, consistent with their outer membrane origin. Purified OMV were shown to be relatively free of inner membrane contamination by the absence of measurable β-NADH oxidase activity and the absence of protoplasmic cylinder-associated proteins observed by Coomassie blue staining. Approximately 60 protein spots (some of which are putative isoelectric isomers) with 25 distinct molecular weights were identified as constituents of the OMV enrichment. The majority of these proteins were also shown to be antigenic with sera from B. hermsii-infected mice. Seven of these antigenic proteins were labeled with [3H]palmitate, including the surface-exposed glycerophosphodiester phosphodiesterase, the variable major proteins 7 and 33, and proteins of 15, 17, 38, 42, and 67 kDa, indicating that they are lipoprotein constituents of the outer membrane. In addition, immunoblot analysis of the OMV probed with antiserum to the Borrelia garinii surface-exposed p66/Oms66 porin protein demonstrated the presence of a p66 (Oms66) outer membrane homolog. Treatment of intact B. hermsii with proteinase K resulted in the partial proteolysis of the Oms66/p66 homolog, indicating that it is surface exposed. This identification and characterization of the OMV proteins should aid in further studies of pathogenesis and immunity of tick-borne relapsing fever.

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Zheng, Jing, Lanlan Li, and Hui Jiang. "Molecular pathways of mitochondrial outer membrane protein degradation." Biochemical Society Transactions 47, no. 5 (October 11, 2019): 1437–47. http://dx.doi.org/10.1042/bst20190275.

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Abstract Mitochondrial outer membrane (MOM) encloses inner compartments of mitochondria and integrates cytoplasmic signals to regulate essential mitochondrial processes, such as protein import, dynamics, metabolism, cell death, etc. A substantial understanding of MOM associated proteostatic stresses and quality control pathways has been obtained in recent years. Six MOM associated protein degradation (MAD) pathways center on three AAA ATPases: Cdc48 in the cytoplasm, Msp1 integral to MOM, and Yme1 integral to the inner membrane. These pathways survey MOM proteome from the cytoplasmic and the inter-membrane space (IMS) sides. They detect and degrade MOM proteins with misfolded cytoplasmic and IMS domains, remove mistargeted tail-anchored proteins, and clear mitochondrial precursor proteins clogged in the TOM import complex. These MOM associated protein quality control pathways collaboratively maintain mitochondrial proteostasis and cell viability.

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40

Gentle, Ian, Kipros Gabriel, Peter Beech, Ross Waller, and Trevor Lithgow. "The Omp85 family of proteins is essential for outer membrane biogenesis in mitochondria and bacteria." Journal of Cell Biology 164, no. 1 (December 29, 2003): 19–24. http://dx.doi.org/10.1083/jcb.200310092.

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Integral proteins in the outer membrane of mitochondria control all aspects of organelle biogenesis, being required for protein import, mitochondrial fission, and, in metazoans, mitochondrial aspects of programmed cell death. How these integral proteins are assembled in the outer membrane had been unclear. In bacteria, Omp85 is an essential component of the protein insertion machinery, and we show that members of the Omp85 protein family are also found in eukaryotes ranging from plants to humans. In eukaryotes, Omp85 is present in the mitochondrial outer membrane. The gene encoding Omp85 is essential for cell viability in yeast, and conditional omp85 mutants have defects that arise from compromised insertion of integral proteins like voltage-dependent anion channel (VDAC) and components of the translocase in the outer membrane of mitochondria (TOM) complex into the mitochondrial outer membrane.

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Boesze-Battaglia, Kathleen, Arlene D. Albert, James S. Frye, and Philip L. Yeagle. "Differential membrane protein phosphorylation in bovine retinal rod outer segment disk membranes as a function of disk age." Bioscience Reports 16, no. 4 (August 1, 1996): 289–97. http://dx.doi.org/10.1007/bf01855013.

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The outer segment portion of photoreceptor rod cells is composed of a stacked array of disk membranes. Newly formed disks are found at the base of the rod outer segment (ROS) and are relatively high in membrane cholesterol. Older disks are found at the apical tip of the ROS and are low in membrane cholesterol. Disk membranes were separated based on their membrane cholesterol content and the extent of membrane protein phosphorylation determined. Light induced phosphorylation of ROS disk membrane proteins was investigated using magic angle spinning31P NMR. When intact rod outer segment preparations were stimulated by light, in the presence of endogenously available kinases, membrane proteins located in disks at the base of the ROS were more heavily phosphorylated than those at the tip. SDS-gel electrophoresis of the phosphorylated disk membranes subpopulations identified a phosphoprotein species with a molecular weight of approximately 68–72 kDa that was more heavily phosphorylated in newly formed disks than in old disks. The identity of this phosphoprotein is presently under investigation. When the phosphorylation reaction was carried out in isolated disk membrane preparations with exogenously added co-factors and kinases, there was no preferential protein phosphorylation. Taken collectively, these results suggest that within the ROS there is a protein phosphorylation gradient that maybe indicative of co-factor or kinase heterogeneity.

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Moon, Dong Chan, Chul Hee Choi, Jung Hwa Lee, Chi-Won Choi, Hye-Yeon Kim, Jeong Soon Park, Seung Il Kim, and Je Chul Lee. "Acinetobacter baumannii outer membrane protein a modulates the biogenesis of outer membrane vesicles." Journal of Microbiology 50, no. 1 (February 2012): 155–60. http://dx.doi.org/10.1007/s12275-012-1589-4.

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43

Hoogerheide, David P., Sergei Y. Noskov, Daniel Jacobs, Lucie Bergdoll, Vitalii Silin, David L. Worcester, Jeff Abramson, Hirsh Nanda, Tatiana K. Rostovtseva, and Sergey M. Bezrukov. "Structural features and lipid binding domain of tubulin on biomimetic mitochondrial membranes." Proceedings of the National Academy of Sciences 114, no. 18 (April 18, 2017): E3622—E3631. http://dx.doi.org/10.1073/pnas.1619806114.

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Dimeric tubulin, an abundant water-soluble cytosolic protein known primarily for its role in the cytoskeleton, is routinely found to be associated with mitochondrial outer membranes, although the structure and physiological role of mitochondria-bound tubulin are still unknown. There is also no consensus on whether tubulin is a peripheral membrane protein or is integrated into the outer mitochondrial membrane. Here the results of five independent techniques—surface plasmon resonance, electrochemical impedance spectroscopy, bilayer overtone analysis, neutron reflectometry, and molecular dynamics simulations—suggest that α-tubulin’s amphipathic helix H10 is responsible for peripheral binding of dimeric tubulin to biomimetic “mitochondrial” membranes in a manner that differentiates between the two primary lipid headgroups found in mitochondrial membranes, phosphatidylethanolamine and phosphatidylcholine. The identification of the tubulin dimer orientation and membrane-binding domain represents an essential step toward our understanding of the complex mechanisms by which tubulin interacts with integral proteins of the mitochondrial outer membrane and is important for the structure-inspired design of tubulin-targeting agents.

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Roller, Richard J., and David C. Johnson. "Herpesvirus Nuclear Egress across the Outer Nuclear Membrane." Viruses 13, no. 12 (November 24, 2021): 2356. http://dx.doi.org/10.3390/v13122356.

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Herpesvirus capsids are assembled in the nucleus and undergo a two-step process to cross the nuclear envelope. Capsids bud into the inner nuclear membrane (INM) aided by the nuclear egress complex (NEC) proteins UL31/34. At that stage of egress, enveloped virions are found for a short time in the perinuclear space. In the second step of nuclear egress, perinuclear enveloped virions (PEVs) fuse with the outer nuclear membrane (ONM) delivering capsids into the cytoplasm. Once in the cytoplasm, capsids undergo re-envelopment in the Golgi/trans-Golgi apparatus producing mature virions. This second step of nuclear egress is known as de-envelopment and is the focus of this review. Compared with herpesvirus envelopment at the INM, much less is known about de-envelopment. We propose a model in which de-envelopment involves two phases: (i) fusion of the PEV membrane with the ONM and (ii) expansion of the fusion pore leading to release of the viral capsid into the cytoplasm. The first phase of de-envelopment, membrane fusion, involves four herpes simplex virus (HSV) proteins: gB, gH/gL, gK and UL20. gB is the viral fusion protein and appears to act to perturb membranes and promote fusion. gH/gL may also have similar properties and appears to be able to act in de-envelopment without gB. gK and UL20 negatively regulate these fusion proteins. In the second phase of de-envelopment (pore expansion and capsid release), an alpha-herpesvirus protein kinase, US3, acts to phosphorylate NEC proteins, which normally produce membrane curvature during envelopment. Phosphorylation of NEC proteins reverses tight membrane curvature, causing expansion of the membrane fusion pore and promoting release of capsids into the cytoplasm.

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Matesic, D. F., N. J. Philp, J. M. Murray, and P. A. Liebman. "Tubulin in bovine retinal rod outer segments." Journal of Cell Science 103, no. 1 (September 1, 1992): 157–66. http://dx.doi.org/10.1242/jcs.103.1.157.

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Bovine rod outer segment (ROS) preparations contain a major 58 kDa protein doublet that was identified by immunoblot as tubulin. Quantification by gel densitometry showed that the total amount of tubulin was 5- to 10-fold higher than that attributable to the rod axoneme, suggesting additional role(s) for tubulin in photoreceptor cells. Approximately 20% of this nonaxonemal tubulin (15% of total tubulin) is tightly associated with outer segment membranes. This fraction remains membrane-associated after extensive low- or high-salt washing, requiring detergents or protein denaturants for release from ROS membranes. Unlike ROS soluble tubulin it associates tightly with liposomes upon detergent solubilization and reconstitution. The ROS membrane-associated tubulin is highly enriched in isolated ROS plasma membrane fractions compared to the total outer segment membrane pool and can be localized to the plasma membrane but not to disks by immunofluorescent staining, suggesting a possible role in the structure or electrophysiology of the rod outer segment plasma membrane.

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Nesper, Jutta, Alexander Brosig, Philippe Ringler, Geetika J. Patel, Shirley A. Müller, Jörg H. Kleinschmidt, Winfried Boos, Kay Diederichs, and Wolfram Welte. "Omp85Tt from Thermus thermophilus HB27: an Ancestral Type of the Omp85 Protein Family." Journal of Bacteriology 190, no. 13 (May 2, 2008): 4568–75. http://dx.doi.org/10.1128/jb.00369-08.

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ABSTRACT Proteins belonging to the Omp85 family are involved in the assembly of β-barrel outer membrane proteins or in the translocation of proteins across the outer membrane in bacteria, mitochondria, and chloroplasts. The cell envelope of the thermophilic bacterium Thermus thermophilus HB27 is multilayered, including an outer membrane that is not well characterized. Neither the precise lipid composition nor much about integral membrane proteins is known. The genome of HB27 encodes one Omp85-like protein, Omp85Tt, representing an ancestral type of this family. We overexpressed Omp85Tt in T. thermophilus and purified it from the native outer membranes. In the presence of detergent, purified Omp85Tt existed mainly as a monomer, composed of two stable protease-resistant modules. Circular dichroism spectroscopy indicated predominantly β-sheet secondary structure. Electron microscopy of negatively stained lipid-embedded Omp85Tt revealed ring-like structures with a central cavity of ∼1.5 nm in diameter. Single-channel conductance recordings indicated that Omp85Tt forms ion channels with two different conducting states, characterized by conductances of ∼0.4 nS and ∼0.65 nS, respectively.

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Jagannadham, M. V., and S. Saranya. "Analysis of the Membrane proteins of an Antarctic Bacterium Pseudomonas Syringae." Proteomics Insights 4 (January 2011): PRI.S5383. http://dx.doi.org/10.4137/pri.s5383.

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The proteins of an Antarctic bacterium Pseudomonas syringae Lz4W, identified earlier by different membrane protein preparation methods, were combined together and the redundant identities removed. In total, 1479 proteins including 148 outer membrane proteins from this bacterium were predicted by the algorithm PSORTb3.0. A detailed analysis on their subcellular localization was undertaken which was determined using TMHMM, TMB-hunt and BOMP. A comparison of PSORTb predicted outer membrane proteins with BOMP, revealed that most of the proteins predicted by the former, contained β–barrels in the outer membranes. A comparative analysis of PSORTb, TMHMM and TMB-hunt reveals that most of the outer membranes proteins of this bacterium could be identified using this approach. Thus, by using a combination of biochemical and different bioinformatics algorithms, the membrane proteins of P. syringae are analyzed. In particular, PSORTb results are compared and supported by other algorithms, to improve the strength of OM proteins prediction. Several proteins, having an important role in cold adaptation of the organism, could also be identified.

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Miller, David J., Michael D. Schwartz, and Paul Ahlquist. "Flock House Virus RNA Replicates on Outer Mitochondrial Membranes in Drosophila Cells." Journal of Virology 75, no. 23 (December 1, 2001): 11664–76. http://dx.doi.org/10.1128/jvi.75.23.11664-11676.2001.

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ABSTRACT The identification and characterization of host cell membranes essential for positive-strand RNA virus replication should provide insight into the mechanisms of viral replication and potentially identify novel targets for broadly effective antiviral agents. The alphanodavirus flock house virus (FHV) is a positive-strand RNA virus with one of the smallest known genomes among animal RNA viruses, and it can replicate in insect, plant, mammalian, and yeast cells. To investigate the localization of FHV RNA replication, we generated polyclonal antisera against protein A, the FHV RNA-dependent RNA polymerase, which is the sole viral protein required for FHV RNA replication. We detected protein A within 4 h after infection ofDrosophila DL-1 cells and, by differential and isopycnic gradient centrifugation, found that protein A was tightly membrane associated, similar to integral membrane replicase proteins from other positive-strand RNA viruses. Confocal immunofluorescence microscopy and virus-specific, actinomycin D-resistant bromo-UTP incorporation identified mitochondria as the intracellular site of protein A localization and viral RNA synthesis. Selective membrane permeabilization and immunoelectron microscopy further localized protein A to outer mitochondrial membranes. Electron microscopy revealed 40- to 60-nm membrane-bound spherical structures in the mitochondrial intermembrane space of FHV-infected cells, similar in ultrastructural appearance to tombusvirus- and togavirus-induced membrane structures. We concluded that FHV RNA replication occurs on outer mitochondrial membranes and shares fundamental biochemical and ultrastructural features with RNA replication of positive-strand RNA viruses from other families.

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Hiltbrunner, A., J. Bauer, M. Alvarez-Huerta, and F. Kessler. "Protein translocon at the Arabidopsis outer chloroplast membrane." Biochemistry and Cell Biology 79, no. 5 (October 1, 2001): 629–35. http://dx.doi.org/10.1139/o01-145.

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Chloroplasts are organelles essential for the photoautotrophic growth of plants. Their biogenesis from undifferentiated proplastids is triggered by light and requires the import of hundreds of different precursor proteins from the cytoplasm. Cleavable N-terminal transit sequences target the precursors to the chloroplast where translocon complexes at the outer (Toc complex) and inner (Tic complex) envelope membranes enable their import. In pea, the Toc complex is trimeric consisting of two surface-exposed GTP-binding proteins (Toc159 and Toc34) involved in precursor recognition and Toc75 forming an aequeous protein-conducting channel. Completion of the Arabidopsis genome has revealed an unexpected complexity of predicted components of the Toc complex in this plant model organism: four genes encode homologs of Toc159, two encode homologs of Toc34, but only one encodes a likely functional homolog of Toc75. The availability of the genomic sequence data and powerful molecular genetic techniques in Arabidopsis set the stage to unravel the mechanisms of chloroplast protein import in unprecedented depth.Key words: Arabidopsis, genetics, chloroplast, protein import.

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Danoff, Emily J., and Karen G. Fleming. "Membrane Defects Accelerate Outer Membrane β-Barrel Protein Folding." Biochemistry 54, no. 2 (December 22, 2014): 97–99. http://dx.doi.org/10.1021/bi501443p.

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Journal articles on the topic 'Outer membrane protein'

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