601
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Peng SE, Wang YB, Wang LH, Chen WNU, Lu CY, Fang LS, Chen CS. Proteomic analysis of symbiosome membranes in Cnidaria-dinoflagellate endosymbiosis. Proteomics 2010; 10:1002-16. [DOI: 10.1002/pmic.200900595] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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602
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Yuan J, Zweers JC, van Dijl JM, Dalbey RE. Protein transport across and into cell membranes in bacteria and archaea. Cell Mol Life Sci 2010; 67:179-99. [PMID: 19823765 PMCID: PMC11115550 DOI: 10.1007/s00018-009-0160-x] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2009] [Revised: 09/13/2009] [Accepted: 09/21/2009] [Indexed: 12/21/2022]
Abstract
In the three domains of life, the Sec, YidC/Oxa1, and Tat translocases play important roles in protein translocation across membranes and membrane protein insertion. While extensive studies have been performed on the endoplasmic reticular and Escherichia coli systems, far fewer studies have been done on archaea, other Gram-negative bacteria, and Gram-positive bacteria. Interestingly, work carried out to date has shown that there are differences in the protein transport systems in terms of the number of translocase components and, in some cases, the translocation mechanisms and energy sources that drive translocation. In this review, we will describe the different systems employed to translocate and insert proteins across or into the cytoplasmic membrane of archaea and bacteria.
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Affiliation(s)
- Jijun Yuan
- Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, OH 43210 USA
| | - Jessica C. Zweers
- Department of Medical Microbiology, University Medical Center Groningen and University of Groningen, Hanzeplein 1, 30001, 9700 RB Groningen, The Netherlands
| | - Jan Maarten van Dijl
- Department of Medical Microbiology, University Medical Center Groningen and University of Groningen, Hanzeplein 1, 30001, 9700 RB Groningen, The Netherlands
| | - Ross E. Dalbey
- Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, OH 43210 USA
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603
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Abstract
Secretory proteins are transported across the bacterial envelope using a membrane protein complex called the SecY channel or translocon. Major advances in understanding this transporter have been accomplished with methods including purification, crystallization, and reconstitution of the translocation reaction in vitro. We here describe the incorporation of the SecY complex into supported nanometer scale lipid bilayers called Nanodiscs. These nanoparticles mimic a membrane environment and circumvent many of the technical problems typically observed with liposomes and detergent micelles. The technology is simple, yet should lead to additional new progresses in the field of membrane protein transport.
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Affiliation(s)
- Kush Dalal
- Department of Biochemistry and Molecular Biology, Life Sciences Institute, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
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604
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Abstract
Global folding of polypeptides entering the endoplasmic reticulum (ER) starts as soon as they emerge from the narrow Sec61 translocon. Attainment of the native structure can take from several minutes to hours, depending on the gene product. Until then, non-native folding intermediates must be protected from molecular chaperones that recognize misfolded determinants and could prematurely interrupt folding programs by re-directing them to disposal pathways. On the other hand, futile folding attempts must actively be stopped to prevent intraluminal accumulation of defective cargo. This review describes recent advances in understanding how terminally misfolded polypeptides are extracted from the folding environment and directed to specific dislocons within the ER membrane for transfer to the cytoplasm for proteasome-mediated degradation.
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605
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Yamagata A, Mimura H, Sato Y, Yamashita M, Yoshikawa A, Fukai S. Structural insight into the membrane insertion of tail-anchored proteins by Get3. Genes Cells 2009; 15:29-41. [PMID: 20015340 DOI: 10.1111/j.1365-2443.2009.01362.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Tail anchored (TA) proteins, which are important for numerous cellular processes, are defined by a single transmembrane domain (TMD) near the C-terminus. The membrane insertion of TA proteins is mediated by the highly conserved ATPase Get3. Here we report the crystal structures of Get3 in ADP-bound and nucleotide-free forms at 3.0 A and 2.8 A resolutions, respectively. Get3 consists of a nucleotide binding domain and a helical domain. Both structures exhibit a Zn(2+)-mediated homodimer in a head-to-head orientation, representing an open dimer conformation. Our cross-link experiments indicated the closed dimer-stimulating ATP hydrolysis, which might be coupled with TA-protein release. Further, our coexpression-based binding assays using a model TA protein Sec22p revealed the direct interaction between the helical domain of Get3 and the Sec22p TMD. This interaction is independent of ATP and dimer formation. Finally, we propose a structural mechanism that links ATP hydrolysis with the TA-protein insertion mediated by the conserved DTAPTGH motif.
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Affiliation(s)
- Atsushi Yamagata
- Structural Biology Laboratory, Life Science Division, Synchrotron Radiation Research Organization and Institute of Molecular and Cellular Biosciences, The University of Tokyo, Tokyo 113-0032, Japan
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606
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A statistical model for translocation of structured polypeptide chains through nanopores. J Phys Chem B 2009; 113:10348-56. [PMID: 19572676 DOI: 10.1021/jp900947f] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The translocation process of a globular protein (ubiquitin) across a cylindrical nanopore is studied via molecular dynamics simulations. The ubiquitin is described by a native-centric model on a Calpha carbon backbone to investigate the influence of protein-like structural properties on the translocation mechanism. A thermodynamical and kinetic characterization of the process is obtained by studying the statistics of blockage times, the mobility, and the translocation probability as a function of the pulling force F acting in the pore. The transport dynamics occurs when the force exceeds a threshold Fc depending on a free-energy barrier that ubiquitin has to overcome in order to slide along the channel. Such a barrier results from competition of the unfolding energy and the entropy associated with the confinement effects of the pore. We implement appropriate umbrella sampling simulations to compute the free-energy profile as a function of the position of the ubiquitin center of mass inside of the channel (reaction coordinate). This free energy is then used to construct a phenomenological drift-diffusion model in the reaction coordinate which explains and reproduces the behavior of the observables during the translocation.
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607
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Targeting of inositol 1,4,5-trisphosphate receptor to the endoplasmic reticulum by its first transmembrane domain. Biochem J 2009; 425:61-9. [PMID: 19845505 PMCID: PMC2805921 DOI: 10.1042/bj20091051] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Targeting of IP3R (inositol 1,4,5-trisphosphate receptors) to membranes of the ER (endoplasmic reticulum) and their retention within ER or trafficking to other membranes underlies their ability to generate spatially organized Ca2+ signals. N-terminal fragments of IP3R1 (type 1 IP3R) were tagged with enhanced green fluorescent protein, expressed in COS-7 cells and their distribution was determined by confocal microscopy and subcellular fractionation. Localization of IP3R1 in the ER requires translation of between 26 and 34 residues beyond the end of the first transmembrane domain (TMD1), a region that includes TMD2 (second transmembrane domain). Replacement of these post-TMD1 residues with unrelated sequences of similar length (24–36 residues) partially mimicked the native residues. We conclude that for IP3R approx. 30 residues after TMD1 must be translated to allow a signal sequence within TMD1 to be extruded from the ribosome and mediate co-translational targeting to the ER. Hydrophobic residues within TMD1 and TMD2 then ensure stable association with the ER membrane.
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608
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Kida Y, Kume C, Hirano M, Sakaguchi M. Environmental transition of signal-anchor sequences during membrane insertion via the endoplasmic reticulum translocon. Mol Biol Cell 2009; 21:418-29. [PMID: 19955210 PMCID: PMC2814787 DOI: 10.1091/mbc.e09-08-0738] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
We determined the environments of polypeptide chains during membrane translocation and integration using site-directed Cys alkylation. Migration of a signal-anchor sequence into the membrane synchronizes with formation of its TM orientation, and the ER translocon can provide the aqueous pathway capable of two hydrophilic chains. In biogenesis of membrane proteins on the endoplasmic reticulum, a protein-conducting channel called the translocon functions in both the membrane translocation of lumenal domains and the integration of transmembrane segments. Here we analyzed the environments of polypeptide chains during the processes by water-dependent alkylation of N-ethylmaleimide at site-directed Cys residues. Using the technique, the region embedded in the hydrophobic portion of the membrane within a signal-anchor sequence and its shortening by insertion of a Pro residue could be detected. When translocation of the N-terminal domain of the signal-anchor was arrested by trapping an N-terminally fused affinity tag sequence, the signal-anchor was susceptible to alkylation, indicating that its migration into the hydrophobic environment was also arrested. Furthermore, when the tag sequence was separated from the signal-anchor by insertion of a hydrophilic sequence, the signal-anchor became inaccessible to alkylation even in the N-terminally trapped state. This suggests that membrane integration of the signal-anchor synchronizes with partial translocation of its N-terminal domain. Additionally, in an integration intermediate of a membrane protein, both of the two translocation-arrested hydrophilic chains were in an aqueous environment flanking the translocon, suggesting that the translocon provides the hydrophilic pathway capable of at least two translocating chains.
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Affiliation(s)
- Yuichiro Kida
- Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan.
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609
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Abbott DA, Zelle RM, Pronk JT, van Maris AJ. Metabolic engineering ofSaccharomyces cerevisiaeâfor production of carboxylic acids: current status and challenges. FEMS Yeast Res 2009; 9:1123-36. [DOI: 10.1111/j.1567-1364.2009.00537.x] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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610
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Signal peptides are allosteric activators of the protein translocase. Nature 2009; 462:363-7. [PMID: 19924216 DOI: 10.1038/nature08559] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Accepted: 10/06/2009] [Indexed: 11/08/2022]
Abstract
Extra-cytoplasmic polypeptides are usually synthesized as 'preproteins' carrying amino-terminal, cleavable signal peptides and secreted across membranes by translocases. The main bacterial translocase comprises the SecYEG protein-conducting channel and the peripheral ATPase motor SecA. Most proteins destined for the periplasm and beyond are exported post-translationally by SecA. Preprotein targeting to SecA is thought to involve signal peptides and chaperones like SecB. Here we show that signal peptides have a new role beyond targeting: they are essential allosteric activators of the translocase. On docking on their binding groove on SecA, signal peptides act in trans to drive three successive states: first, 'triggering' that drives the translocase to a lower activation energy state; second, 'trapping' that engages non-native preprotein mature domains docked with high affinity on the secretion apparatus; and third, 'secretion' during which trapped mature domains undergo several turnovers of translocation in segments. A significant contribution by mature domains renders signal peptides less critical in bacterial secretory protein targeting than currently assumed. Rather, it is their function as allosteric activators of the translocase that renders signal peptides essential for protein secretion. A role for signal peptides and targeting sequences as allosteric activators may be universal in protein translocases.
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611
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Structural insights into tail-anchored protein binding and membrane insertion by Get3. Proc Natl Acad Sci U S A 2009; 106:21131-6. [PMID: 19948960 DOI: 10.1073/pnas.0910223106] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Tail-anchored (TA) membrane proteins are involved in a variety of important cellular functions, including membrane fusion, protein translocation, and apoptosis. The ATPase Get3 (Asna1, TRC40) was identified recently as the endoplasmic reticulum targeting factor of TA proteins. Get3 consists of an ATPase and alpha-helical subdomain enriched in methionine and glycine residues. We present structural and biochemical analyses of Get3 alone as well as in complex with a TA protein, ribosome-associated membrane protein 4 (Ramp4). The ATPase domains form an extensive dimer interface that encloses 2 nucleotides in a head-to-head orientation and a zinc ion. Amide proton exchange mass spectrometry shows that the alpha-helical subdomain of Get3 displays considerable flexibility in solution and maps the TA protein-binding site to the alpha-helical subdomain. The non-hydrolyzable ATP analogue AMPPNP-Mg(2+)- and ADP-Mg(2+)-bound crystal structures representing the pre- and posthydrolysis states are both in a closed form. In the absence of a TA protein cargo, ATP hydrolysis does not seem to be possible. Comparison with the ADP.AlF(4)(-)-bound structure representing the transition state (Mateja A, et al. (2009) Nature 461:361-366) indicates how the presence of a TA protein is communicated to the ATP-binding site. In vitro membrane insertion studies show that recombinant Get3 inserts Ramp4 in a nucleotide- and receptor-dependent manner. Although ATP hydrolysis is not required for Ramp4 insertion per se, it seems to be required for efficient insertion. We postulate that ATP hydrolysis is needed to release Get3 from its receptor. Taken together, our results provide mechanistic insights into posttranslational targeting of TA membrane proteins by Get3.
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612
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Mapping polypeptide interactions of the SecA ATPase during translocation. Proc Natl Acad Sci U S A 2009; 106:20800-5. [PMID: 19933328 DOI: 10.1073/pnas.0910550106] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many bacterial proteins, including most secretory proteins, are translocated across the plasma membrane by the interplay of the cytoplasmic SecA ATPase and a protein-conducting channel formed by the SecY complex. SecA catalyzes the sequential movement of polypeptide segments through the SecY channel. How SecA interacts with a broad range of polypeptide segments is unclear, but structural data raise the possibility that translocation substrates bind into a "clamp" of SecA. Here, we have used disulfide bridge cross-linking to test this hypothesis. To analyze polypeptide interactions of SecA during translocation, two cysteines were introduced into a translocation intermediate: one that cross-links to the SecY channel and the other one for cross-linking to a cysteine placed at various positions in SecA. Our results show that a translocating polypeptide is indeed captured inside SecA's clamp and moves in an extended conformation through the clamp into the SecY channel. These results define the polypeptide path during SecA-mediated protein translocation and suggest a mechanism by which ATP hydrolysis by SecA is used to move a polypeptide chain through the SecY channel.
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613
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Cross BCS, McKibbin C, Callan AC, Roboti P, Piacenti M, Rabu C, Wilson CM, Whitehead R, Flitsch SL, Pool MR, High S, Swanton E. Eeyarestatin I inhibits Sec61-mediated protein translocation at the endoplasmic reticulum. J Cell Sci 2009; 122:4393-400. [PMID: 19903691 DOI: 10.1242/jcs.054494] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Production and trafficking of proteins entering the secretory pathway of eukaryotic cells is coordinated at the endoplasmic reticulum (ER) in a process that begins with protein translocation via the membrane-embedded ER translocon. The same complex is also responsible for the co-translational integration of membrane proteins and orchestrates polypeptide modifications that are often essential for protein function. We now show that the previously identified inhibitor of ER-associated degradation (ERAD) eeyarestatin 1 (ES(I)) is a potent inhibitor of protein translocation. We have characterised this inhibition of ER translocation both in vivo and in vitro, and provide evidence that ES(I) targets a component of the Sec61 complex that forms the membrane pore of the ER translocon. Further analyses show that ES(I) acts by preventing the transfer of the nascent polypeptide from the co-translational targeting machinery to the Sec61 complex. These results identify a novel effect of ES(I), and suggest that the drug can modulate canonical protein transport from the cytosol into the mammalian ER both in vitro and in vivo.
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Affiliation(s)
- Benedict C S Cross
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester, M13 9PT, UK
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614
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Pearse BR, Hebert DN. Lectin chaperones help direct the maturation of glycoproteins in the endoplasmic reticulum. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1803:684-93. [PMID: 19891995 DOI: 10.1016/j.bbamcr.2009.10.008] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 08/27/2009] [Revised: 10/09/2009] [Accepted: 10/20/2009] [Indexed: 02/06/2023]
Abstract
Eukaryotic secretory pathway cargo fold to their native structures within the confines of the endoplasmic reticulum (ER). To ensure a high degree of folding fidelity, a multitude of covalent and noncovalent constraints are imparted upon nascent proteins. These constraints come in the form of topological restrictions or membrane tethers, covalent modifications, and interactions with a series of molecular chaperones. N-linked glycosylation provides inherent benefits to proper folding and creates a platform for interactions with specific chaperones and Cys modifying enzymes. Recent insights into this timeline of protein maturation have revealed mechanisms for protein glycosylation and iterative targeting of incomplete folding intermediates, which provides nurturing interactions with molecular chaperones that assist in the efficient maturation of proteins in the eukaryotic secretory pathway.
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Affiliation(s)
- Bradley R Pearse
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA 01003, USA
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615
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Becker T, Bhushan S, Jarasch A, Armache JP, Funes S, Jossinet F, Gumbart J, Mielke T, Berninghausen O, Schulten K, Westhof E, Gilmore R, Mandon EC, Beckmann R. Structure of monomeric yeast and mammalian Sec61 complexes interacting with the translating ribosome. Science 2009; 326:1369-73. [PMID: 19933108 DOI: 10.1126/science.1178535] [Citation(s) in RCA: 222] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The trimeric Sec61/SecY complex is a protein-conducting channel (PCC) for secretory and membrane proteins. Although Sec complexes can form oligomers, it has been suggested that a single copy may serve as an active PCC. We determined subnanometer-resolution cryo-electron microscopy structures of eukaryotic ribosome-Sec61 complexes. In combination with biochemical data, we found that in both idle and active states, the Sec complex is not oligomeric and interacts mainly via two cytoplasmic loops with the universal ribosomal adaptor site. In the active state, the ribosomal tunnel and a central pore of the monomeric PCC were occupied by the nascent chain, contacting loop 6 of the Sec complex. This provides a structural basis for the activity of a solitary Sec complex in cotranslational protein translocation.
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Affiliation(s)
- Thomas Becker
- Gene Center Munich and Center for Integrated Protein Science, Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
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616
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Zimmer J, Rapoport TA. Conformational flexibility and peptide interaction of the translocation ATPase SecA. J Mol Biol 2009; 394:606-12. [PMID: 19850053 PMCID: PMC2832196 DOI: 10.1016/j.jmb.2009.10.024] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2009] [Revised: 10/08/2009] [Accepted: 10/09/2009] [Indexed: 11/26/2022]
Abstract
The SecA ATPase forms a functional complex with the protein-conducting SecY channel to translocate polypeptides across the bacterial cell membrane. SecA recognizes the translocation substrate and catalyzes its unidirectional movement through the SecY channel. The recent crystal structure of the Thermotoga maritima SecA-SecYEG complex shows the ATPase in a conformation where the nucleotide-binding domains (NBDs) have closed around a bound ADP-BeFx complex and SecA's polypeptide-binding clamp is shut. Here, we present the crystal structure of T. maritima SecA in isolation, determined in its ADP-bound form at 3.1 A resolution. SecA alone has a drastically different conformation in which the nucleotide-binding pocket between NBD1 and NBD2 is open and the preprotein cross-linking domain has rotated away from both NBDs, thereby opening the polypeptide-binding clamp. To investigate how this clamp binds polypeptide substrates, we also determined a structure of Bacillus subtilis SecA in complex with a peptide at 2.5 A resolution. This structure shows that the peptide augments the highly conserved beta-sheet at the back of the clamp. Taken together, these structures suggest a mechanism by which ATP hydrolysis can lead to polypeptide translocation.
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Affiliation(s)
- Jochen Zimmer
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
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617
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Donnellan PD, Kinsella BT. Immature and mature species of the human Prostacyclin Receptor are ubiquitinated and targeted to the 26S proteasomal or lysosomal degradation pathways, respectively. J Mol Signal 2009; 4:7. [PMID: 19781057 PMCID: PMC2760523 DOI: 10.1186/1750-2187-4-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2009] [Accepted: 09/25/2009] [Indexed: 12/22/2022] Open
Abstract
Background The human prostacyclin receptor (hIP) undergoes agonist-induced phosphorylation, desensitisation and internalisation and may be recycled to the plasma membrane or targeted for degradation by, as yet, unknown mechanism(s). Results Herein it was sought to investigate the turnover of the hIP under basal conditions and in response to cicaprost stimulation. It was established that the hIP is subject to low-level basal degradation but, following agonist stimulation, degradation is substantially enhanced. Inhibition of the lysosomal pathway prevented basal and agonist-induced degradation of the mature species of the hIP (46-66 kDa). Conversely, inhibition of the proteasomal pathway had no effect on levels of the mature hIP but led to time-dependent accumulation of four newly synthesised immature species (38-44 kDa). It was established that both the mature and immature species of the hIP may be polyubiquitinated and this modification may be required for lysosomal sorting of the mature, internalised receptors and for degradation of the immature receptors by the 26S proteasomes through the ER-associated degradation (ERAD) process, respectively. Moreover, these data substantially advance knowledge of the factors regulating processing and maturation of the hIP, a complex receptor subject to multiple post-translational modifications including N-glycosylation, phosphorylation, isoprenylation, palmitoylation, in addition to polyubiquitination, as determined herein. Conclusion These findings indicate that the hIP is post-translationally modified by ubiquitination, which targets the immature species to the 26S proteasomal degradation pathway and the mature species to the lysosomal degradation pathway.
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Affiliation(s)
- Peter D Donnellan
- School of Biomolecular and Biomedical Sciences, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland.
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618
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Chiba S, Lamsa A, Pogliano K. A ribosome-nascent chain sensor of membrane protein biogenesis in Bacillus subtilis. EMBO J 2009; 28:3461-75. [PMID: 19779460 DOI: 10.1038/emboj.2009.280] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2009] [Accepted: 08/12/2009] [Indexed: 11/09/2022] Open
Abstract
Proteins in the YidC/Oxa1/Alb3 family have essential functions in membrane protein insertion and folding. Bacillus subtilis encodes two YidC homologs, one that is constitutively expressed (spoIIIJ/yidC1) and a second (yqjG/yidC2) that is induced in spoIIIJ mutants. Regulated induction of yidC2 allows B. subtilis to maintain capacity of the membrane protein insertion pathway. We here show that a gene located upstream of yidC2 (mifM/yqzJ) serves as a sensor of SpoIIIJ activity that regulates yidC2 translation. Decreased SpoIIIJ levels or deletion of the MifM transmembrane domain arrests mifM translation and unfolds an mRNA hairpin that otherwise blocks initiation of yidC2 translation. This regulated translational arrest and yidC2 induction require a specific interaction between the MifM C-terminus and the ribosomal polypeptide exit tunnel. MifM therefore acts as a ribosome-nascent chain complex rather than as a fully synthesized protein. B. subtilis MifM and the previously described secretion monitor SecM in Escherichia coli thereby provide examples of the parallel evolution of two regulatory nascent chains that monitor different protein export pathways by a shared molecular mechanism.
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Affiliation(s)
- Shinobu Chiba
- Division of Biological Sciences, University of California, San Diego, CA, USA
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619
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Taylor CW, Pantazaka E. Targeting and clustering of IP3 receptors: key determinants of spatially organized Ca2+ signals. CHAOS (WOODBURY, N.Y.) 2009; 19:037102. [PMID: 19798811 DOI: 10.1063/1.3127593] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Inositol 1,4,5-trisphosphate receptors (IP3R) are intracellular Ca2+ channels that are almost ubiquitously expressed in animal cells. The spatiotemporal complexity of the Ca2+ signals evoked by IP3R underlies their versatility in cellular signaling. Here we review the mechanisms that contribute to the subcellular targeting of IP3R and the dynamic interplay between IP3R that underpin their ability to generate complex intracellular Ca2+ signals.
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620
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van Stelten J, Silva F, Belin D, Silhavy TJ. Effects of antibiotics and a proto-oncogene homolog on destruction of protein translocator SecY. Science 2009; 325:753-6. [PMID: 19661432 DOI: 10.1126/science.1172221] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Protein secretion occurs via translocation by the evolutionarily conserved Sec complex. LacZ hybrid proteins have long been used to study translocation in Escherichia coli. Some LacZ hybrids were thought to block secretion by physically jamming the Sec complex, leading to cell death. We found that jammed Sec complexes caused the degradation of essential translocator components by the protease FtsH. Increasing the amounts or the stability of the membrane protein YccA, a known inhibitor of FtsH, counteracted this destruction. Antibiotics that inhibit translation elongation also jammed the translocator and caused the degradation of translocator components, which may contribute to their effectiveness. Intriguingly, YccA is a functional homolog of the proto-oncogene product Bax Inhibitor-1, which may share a similar mechanism of action in regulating apoptosis upon prolonged secretion stress.
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Affiliation(s)
- Johna van Stelten
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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621
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Mateja A, Szlachcic A, Downing ME, Dobosz M, Mariappan M, Hegde RS, Keenan RJ. The structural basis of tail-anchored membrane protein recognition by Get3. Nature 2009; 461:361-6. [PMID: 19675567 DOI: 10.1038/nature08319] [Citation(s) in RCA: 139] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2009] [Accepted: 07/27/2009] [Indexed: 11/09/2022]
Abstract
Targeting of newly synthesized membrane proteins to the endoplasmic reticulum is an essential cellular process. Most membrane proteins are recognized and targeted co-translationally by the signal recognition particle. However, nearly 5% of membrane proteins are 'tail-anchored' by a single carboxy-terminal transmembrane domain that cannot access the co-translational pathway. Instead, tail-anchored proteins are targeted post-translationally by a conserved ATPase termed Get3. The mechanistic basis for tail-anchored protein recognition or targeting by Get3 is not known. Here we present crystal structures of yeast Get3 in 'open' (nucleotide-free) and 'closed' (ADP.AlF(4)(-)-bound) dimer states. In the closed state, the dimer interface of Get3 contains an enormous hydrophobic groove implicated by mutational analyses in tail-anchored protein binding. In the open state, Get3 undergoes a striking rearrangement that disrupts the groove and shields its hydrophobic surfaces. These data provide a molecular mechanism for nucleotide-regulated binding and release of tail-anchored proteins during their membrane targeting by Get3.
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Affiliation(s)
- Agnieszka Mateja
- Department of Biochemistry & Molecular Biology, The University of Chicago, Gordon Center for Integrative Science, Room W238, 929 East 57th Street, Chicago, Illinois 60637, USA
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622
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Affiliation(s)
- Eefjan Breukink
- Department of Chemical Biology and Organic Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, Netherlands
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623
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Civelek M, Manduchi E, Riley RJ, Stoeckert CJ, Davies PF. Chronic endoplasmic reticulum stress activates unfolded protein response in arterial endothelium in regions of susceptibility to atherosclerosis. Circ Res 2009; 105:453-61. [PMID: 19661457 DOI: 10.1161/circresaha.109.203711] [Citation(s) in RCA: 173] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
RATIONALE Endothelial function and dysfunction are central to the focal origin and regional development of atherosclerosis; however, an in vivo endothelial phenotypic footprint of susceptibility to atherosclerosis preceding pathological change remains elusive. OBJECTIVE To conduct a comparative multi-site genomics study of arterial endothelial phenotype in atherosusceptible and atheroprotected regions. METHODS AND RESULTS Transcript profiles of freshly isolated endothelial cells from 7 discrete arterial regions in normal swine were analyzed to determine the steady state in vivo endothelial phenotypes in regions of varying susceptibilities to atherosclerosis. The most abundant common feature of the endothelium of all atherosusceptible regions was the upregulation of genes associated with endoplasmic reticulum (ER) stress. The unfolded protein response pathway, induced by ER stress, was therefore investigated in detail in endothelium of the atherosusceptible aortic arch and was found to be partially activated. ER transmembrane signal transducers IRE1alpha and ATF6alpha and their downstream effectors, but not PERK, were activated concomitant with a higher transcript expression of protein folding enzymes and chaperones, indicative of ER stress in vivo. CONCLUSIONS The findings demonstrate the prevalence of chronic endothelial ER stress and activated unfolded protein response in vivo at atherosusceptible arterial sites. We propose that chronic localized biological stress is linked to spatial susceptibility of the endothelium to the initiation of atherosclerosis.
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Affiliation(s)
- Mete Civelek
- Institute for Medicine and Engineering, University of Pennsylvania, 1010 Vagelos Laboratories, 3340 Smith Walk, Philadelphia, PA 19104, USA
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624
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Hessa T, Reithinger JH, von Heijne G, Kim H. Analysis of transmembrane helix integration in the endoplasmic reticulum in S. cerevisiae. J Mol Biol 2009; 386:1222-8. [PMID: 19452628 DOI: 10.1016/j.jmb.2009.01.027] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
What sequence features in integral membrane proteins determine which parts of the polypeptide chain will form transmembrane alpha-helices and which parts will be located outside the lipid bilayer? Previous studies on the integration of model transmembrane segments into the mammalian endoplasmic reticulum (ER) have provided a rather detailed quantitative picture of the relation between amino acid sequence and membrane-integration propensity for proteins targeted to the Sec61 translocon. We have now carried out a comparative study of the integration of N out-C in-orientated 19-residue-long polypeptide segments into the ER of the yeast Saccharomyces cerevisiae. We find that the 'threshold hydrophobicity' required for insertion into the ER membrane is very similar in S. cerevisiae and in mammalian cells. Further, when comparing the contributions to the apparent free energy of membrane insertion of the 20 natural amino acids between the S. cerevisiae and the mammalian ER, we find that the two scales are strongly correlated but that the absolute difference between the most hydrophobic and most hydrophilic residues is approximately 2-fold smaller in S. cerevisiae.
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Affiliation(s)
- Tara Hessa
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
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625
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Tartakoff AM, Tao T. Comparative and evolutionary aspects of macromolecular translocation across membranes. Int J Biochem Cell Biol 2009; 42:214-29. [PMID: 19643202 DOI: 10.1016/j.biocel.2009.07.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2009] [Revised: 07/21/2009] [Accepted: 07/21/2009] [Indexed: 01/10/2023]
Abstract
Membrane barriers preserve the integrity of organelles of eukaryotic cells, yet the genesis and ongoing functions of the same organelles requires that their limiting membranes allow import and export of selected macromolecules. Multiple distinct mechanisms are used for this purpose, only some of which have been traced to prokaryotes. Some can accommodate both monomeric and also large heterooligomeric cargoes. The best characterized of these is nucleocytoplasmic transport. This synthesis compares the unidirectional and bidirectional mechanisms of macromolecular transport of the endoplasmic reticulum, mitochondria, peroxisomes and the nucleus, calls attention to the powerful experimental approaches which have been used for their elucidation, discusses their regulation and evolutionary origins, and highlights relatively unexplored areas.
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Affiliation(s)
- Alan M Tartakoff
- Department of Pathology & Cell Biology Program, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA.
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626
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Abstract
The topology of polytopic membrane proteins is determined by topogenic sequences in the protein, protein-translocon interactions, and interactions during folding within the protein and between the protein and the lipid environment. Orientation of transmembrane domains is dependent on membrane phospholipid composition during initial assembly as well as on changes in lipid composition postassembly. The membrane translocation potential of negative amino acids working in opposition to the positive-inside rule is largely dampened by the normal presence of phosphatidylethanolamine, thus explaining the dominance of positive residues as retention signals. Phosphatidylethanolamine provides the appropriate charge density that permits the membrane surface to maintain a charge balance between membrane translocation and retention signals and also allows the presence of negative residues in the cytoplasmic face of proteins for other purposes.
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Affiliation(s)
- William Dowhan
- Department of Biochemistry and Molecular Biology, University of Texas-Houston Medical School, Houston, TX 77030, USA.
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627
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Colombo SF, Longhi R, Borgese N. The role of cytosolic proteins in the insertion of tail-anchored proteins into phospholipid bilayers. J Cell Sci 2009; 122:2383-92. [DOI: 10.1242/jcs.049460] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Tail-anchored (TA) proteins are membrane proteins that contain an N-terminal domain exposed to the cytosol and a single transmembrane segment near the C-terminus followed by few or no polar residues. TA proteins with a mildly hydrophobic transmembrane domain, such as cytochrome b5 (b5), are able to insert post-translationally into pure lipid vesicles without assistance from membrane proteins. Here, we investigated whether any cytosolic proteins are needed to maintain b5 in a competent state for transmembrane integration. Using b5 constructs translated in vitro or produced in bacteria, we demonstrate that cytosolic proteins are neither necessary nor facilitatory for the unassisted translocation of b5. Furthermore, we demonstrate that no cytosolic protein is involved in the translocation of a C-terminal domain of 85 residues appended to the transmembrane domain of b5. Nevertheless, b5 does bind cytosolic proteins, and in their presence but not in their absence, its insertion into liposomes is inhibited by the thiol oxidant diamide and the alkylating agent N-ethylmaleimide. The effect of diamide is also observed in living cells. Thus, the specific in vivo targeting of b5 might be achieved by interaction with redox-sensitive targeting factors that hinder its nonspecific insertion into any permissive bilayer.
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Affiliation(s)
- Sara F. Colombo
- CNR Institute for Neuroscience and Department of Pharmacology, Università degli Studi di Milano, Italy
| | - Renato Longhi
- CNR Institute of Chemistry of Molecular Recognition, Milano, Italy
| | - Nica Borgese
- CNR Institute for Neuroscience and Department of Pharmacology, Università degli Studi di Milano, Italy
- Department of Pharmacobiological Science, University of Catanzaro `Magna Graecia', Roccelletta di Borgia (CZ), Italy
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628
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Yang JC, Madupu R, Durkin AS, Ekborg NA, Pedamallu CS, Hostetler JB, Radune D, Toms BS, Henrissat B, Coutinho PM, Schwarz S, Field L, Trindade-Silva AE, Soares CAG, Elshahawi S, Hanora A, Schmidt EW, Haygood MG, Posfai J, Benner J, Madinger C, Nove J, Anton B, Chaudhary K, Foster J, Holman A, Kumar S, Lessard PA, Luyten YA, Slatko B, Wood N, Wu B, Teplitski M, Mougous JD, Ward N, Eisen JA, Badger JH, Distel DL. The complete genome of Teredinibacter turnerae T7901: an intracellular endosymbiont of marine wood-boring bivalves (shipworms). PLoS One 2009; 4:e6085. [PMID: 19568419 PMCID: PMC2699552 DOI: 10.1371/journal.pone.0006085] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2009] [Accepted: 05/06/2009] [Indexed: 12/02/2022] Open
Abstract
Here we report the complete genome sequence of Teredinibacter turnerae T7901. T. turnerae is a marine gamma proteobacterium that occurs as an intracellular endosymbiont in the gills of wood-boring marine bivalves of the family Teredinidae (shipworms). This species is the sole cultivated member of an endosymbiotic consortium thought to provide the host with enzymes, including cellulases and nitrogenase, critical for digestion of wood and supplementation of the host's nitrogen-deficient diet. T. turnerae is closely related to the free-living marine polysaccharide degrading bacterium Saccharophagus degradans str. 2–40 and to as yet uncultivated endosymbionts with which it coexists in shipworm cells. Like S. degradans, the T. turnerae genome encodes a large number of enzymes predicted to be involved in complex polysaccharide degradation (>100). However, unlike S. degradans, which degrades a broad spectrum (>10 classes) of complex plant, fungal and algal polysaccharides, T. turnerae primarily encodes enzymes associated with deconstruction of terrestrial woody plant material. Also unlike S. degradans and many other eubacteria, T. turnerae dedicates a large proportion of its genome to genes predicted to function in secondary metabolism. Despite its intracellular niche, the T. turnerae genome lacks many features associated with obligate intracellular existence (e.g. reduced genome size, reduced %G+C, loss of genes of core metabolism) and displays evidence of adaptations common to free-living bacteria (e.g. defense against bacteriophage infection). These results suggest that T. turnerae is likely a facultative intracellular ensosymbiont whose niche presently includes, or recently included, free-living existence. As such, the T. turnerae genome provides insights into the range of genomic adaptations associated with intracellular endosymbiosis as well as enzymatic mechanisms relevant to the recycling of plant materials in marine environments and the production of cellulose-derived biofuels.
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Affiliation(s)
- Joyce C. Yang
- Ocean Genome Legacy, Inc., Ipswich, Massachusetts, United States of America
| | - Ramana Madupu
- J. Craig Venter Institute, San Diego, California, United States of America
| | - A. Scott Durkin
- J. Craig Venter Institute, San Diego, California, United States of America
| | - Nathan A. Ekborg
- Ocean Genome Legacy, Inc., Ipswich, Massachusetts, United States of America
| | | | | | - Diana Radune
- J. Craig Venter Institute, San Diego, California, United States of America
| | - Bradley S. Toms
- J. Craig Venter Institute, San Diego, California, United States of America
| | - Bernard Henrissat
- Architecture et Fonction des Macromolécules Biologiques, UMR6098, CNRS, Universités Aix-Marseille I & II, Case 932, Marseille, France
| | - Pedro M. Coutinho
- Architecture et Fonction des Macromolécules Biologiques, UMR6098, CNRS, Universités Aix-Marseille I & II, Case 932, Marseille, France
| | - Sandra Schwarz
- Department of Microbiology, University of Washington, Seattle, Washington, United States of America
| | - Lauren Field
- New England Biolabs, Ipswich, Massachusetts, United States of America
| | - Amaro E. Trindade-Silva
- Universidade Federal do Rio de Janeiro, Instituto de Biologia, Ilha do Fundao, CCS, Rio de Janeiro, Rio de Janeiro, Brazil
| | - Carlos A. G. Soares
- Universidade Federal do Rio de Janeiro, Instituto de Biologia, Ilha do Fundao, CCS, Rio de Janeiro, Rio de Janeiro, Brazil
| | - Sherif Elshahawi
- Department of Environmental and Biomolecular Systems, OGI School of Science & Engineering, Oregon Health & Science University, Beaverton, Oregon, United States of America
| | - Amro Hanora
- Department of Microbiology and Immunology, Faculty of Pharmacy, Suez Canal University, Ismailia, Egypt
| | - Eric W. Schmidt
- College of Pharmacy, University of Utah, Salt Lake City, Utah, United States of America
| | - Margo G. Haygood
- Department of Environmental and Biomolecular Systems, OGI School of Science & Engineering, Oregon Health & Science University, Beaverton, Oregon, United States of America
| | - Janos Posfai
- New England Biolabs, Ipswich, Massachusetts, United States of America
| | - Jack Benner
- New England Biolabs, Ipswich, Massachusetts, United States of America
| | | | - John Nove
- Ocean Genome Legacy, Inc., Ipswich, Massachusetts, United States of America
| | - Brian Anton
- New England Biolabs, Ipswich, Massachusetts, United States of America
| | - Kshitiz Chaudhary
- New England Biolabs, Ipswich, Massachusetts, United States of America
| | - Jeremy Foster
- New England Biolabs, Ipswich, Massachusetts, United States of America
| | - Alex Holman
- New England Biolabs, Ipswich, Massachusetts, United States of America
| | - Sanjay Kumar
- New England Biolabs, Ipswich, Massachusetts, United States of America
| | - Philip A. Lessard
- Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Yvette A. Luyten
- Ocean Genome Legacy, Inc., Ipswich, Massachusetts, United States of America
- New England Biolabs, Ipswich, Massachusetts, United States of America
| | - Barton Slatko
- New England Biolabs, Ipswich, Massachusetts, United States of America
| | - Nicole Wood
- Ocean Genome Legacy, Inc., Ipswich, Massachusetts, United States of America
| | - Bo Wu
- New England Biolabs, Ipswich, Massachusetts, United States of America
| | - Max Teplitski
- University of Florida, Gainesville, Florida, United States of America
| | - Joseph D. Mougous
- Department of Microbiology, University of Washington, Seattle, Washington, United States of America
| | - Naomi Ward
- Department of Molecular Biology, University of Wyoming, Laramie, Wyoming, United States of America
| | - Jonathan A. Eisen
- UC Davis Genome Center, University of California Davis, Davis, California, United States of America
| | - Jonathan H. Badger
- J. Craig Venter Institute, San Diego, California, United States of America
| | - Daniel L. Distel
- Ocean Genome Legacy, Inc., Ipswich, Massachusetts, United States of America
- * E-mail:
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629
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Dvir H, Choe S. Bacterial expression of a eukaryotic membrane protein in fusion to various Mistic orthologs. Protein Expr Purif 2009; 68:28-33. [PMID: 19524676 DOI: 10.1016/j.pep.2009.06.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2009] [Revised: 05/27/2009] [Accepted: 06/08/2009] [Indexed: 11/30/2022]
Abstract
Mistic, a bacterial membrane-associating protein family, uniquely found in Bacillus species. It enhances expression of eukaryotic membrane proteins at the bacterial membrane. Mistic from B. subtilis (M110), expresses at the Escherichia coli membrane, however its shorter orthologs have been recently shown to be mainly cytoplasmic with varying membrane affinities. Based on that, we hypothesized that the expression level of membrane proteins fused to Mistic is correlated with the degree of membrane association of the particular Mistic protein. We compared expression levels by various Mistic proteins as fusion partners for the Aplysia californica Kv1.1 (aKv1.1) channel as a cargo membrane protein. Mistic from B. atrophaeus (M4), which has the highest membrane association among the shorter orthologs, enhanced expression of the transmembrane domain of aKv1.1 to the highest extent. In contrast, M1, which consists of the 84 C-terminal amino acids of M110 is the most soluble protein and showed the least capacity to express the channel. A chimeric Mistic, constructed with the first alpha-helix (H1) of M110 N-terminally fused to M4, did not increase the level of expression of aKv1.1 beyond those of either the M110 or the M4 fusions. The channel fused to M110, M4 or the aforementioned H1-M4 chimera, expresses in the highest quantity and quality among Mistic proteins, providing suitable sample for structural studies. Our data support the concept that expression levels of 'Misticated' membrane proteins are related to the independent chaperoning character of Mistic via direct membrane association, rather than related to specific sequence-dependent interaction with the E. coli translocon machinery.
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Affiliation(s)
- Hay Dvir
- Structural Biology Laboratory, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA
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630
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Kohler R, Boehringer D, Greber B, Bingel-Erlenmeyer R, Collinson I, Schaffitzel C, Ban N. YidC and Oxa1 form dimeric insertion pores on the translating ribosome. Mol Cell 2009; 34:344-53. [PMID: 19450532 DOI: 10.1016/j.molcel.2009.04.019] [Citation(s) in RCA: 98] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2009] [Revised: 03/09/2009] [Accepted: 04/16/2009] [Indexed: 11/19/2022]
Abstract
The YidC/Oxa1/Alb3 family of membrane proteins facilitates the insertion and assembly of membrane proteins in bacteria, mitochondria, and chloroplasts. Here we present the structures of both Escherichia coli YidC and Saccharomyces cerevisiae Oxa1 bound to E. coli ribosome nascent chain complexes determined by cryo-electron microscopy. Dimers of YidC and Oxa1 are localized above the exit of the ribosomal tunnel. Crosslinking experiments show that the ribosome specifically stabilizes the dimeric state. Functionally important and conserved transmembrane helices of YidC and Oxa1 were localized at the dimer interface by cysteine crosslinking. Both Oxa1 and YidC dimers contact the ribosome at ribosomal protein L23 and conserved rRNA helices 59 and 24, similarly to what was observed for the nonhomologous SecYEG translocon. We suggest that dimers of the YidC and Oxa1 proteins form insertion pores and share a common overall architecture with the SecY monomer.
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Affiliation(s)
- Rebecca Kohler
- Institute of Molecular Biology and Biophysics, ETH Zürich, Zürich, Switzerland
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631
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Dalal K, Duong F. The SecY complex forms a channel capable of ionic discrimination. EMBO Rep 2009; 10:762-8. [PMID: 19483671 DOI: 10.1038/embor.2009.87] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2008] [Revised: 03/10/2009] [Accepted: 03/23/2009] [Indexed: 11/09/2022] Open
Abstract
Protein translocation across the bacterial membrane occurs at the SecY complex or channel. The resting SecY channel is impermeable to small molecules owing to a plug domain that creates a seal. Here, we report that a channel loosely sealed, or with a plug locked open, does not, however, lead to general membrane permeability. Instead, strong selectivity towards small monovalent anions, especially chloride, is observed. Mutations in the pore ring-structure increase both the translocation activity of the channel and its ionic conductance, however the selectivity is maintained. The same ionic specificity also occurs at the onset of protein translocation and across the archaeal SecY complex. Thus, the ion-conducting characteristic of the channel seems to be conserved as a normal consequence of protein translocation. We propose that the pore ring-structure forms a selectivity filter, allowing cells to tolerate channels with imperfect plugs.
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Affiliation(s)
- Kush Dalal
- Department of Biochemistry and Molecular Biology, Life Sciences Institute, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
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632
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Pool MR. A trans-membrane segment inside the ribosome exit tunnel triggers RAMP4 recruitment to the Sec61p translocase. ACTA ACUST UNITED AC 2009; 185:889-902. [PMID: 19468070 PMCID: PMC2711601 DOI: 10.1083/jcb.200807066] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Membrane protein integration occurs predominantly at the endoplasmic reticulum and is mediated by the translocon, which is formed by the Sec61p complex. The translocon binds to the ribosome at the polypeptide exit site such that integration occurs in a cotranslational manner. Ribosomal protein Rpl17 is positioned such that it contacts both the ribosome exit tunnel and the surface of the ribosome near the exit site, where it is intimately associated with the translocon. The presence of a trans-membrane (TM) segment inside the ribosomal exit tunnel leads to the recruitment of RAMP4 to the translocon at a site adjacent to Rpl17. This suggests a signaling function for Rpl17 such that it can recognize a TM segment inside the ribosome and triggers rearrangements of the translocon, priming it for subsequent TM segment integration.
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Affiliation(s)
- Martin R Pool
- Faculty of Life Sciences, University of Manchester, Manchester M139PT, England, UK.
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633
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Johnson AE. The structural and functional coupling of two molecular machines, the ribosome and the translocon. ACTA ACUST UNITED AC 2009; 185:765-7. [PMID: 19468072 PMCID: PMC2711596 DOI: 10.1083/jcb.200902014] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ribosomes synthesizing secretory and membrane proteins are bound to translocons at the membrane of the endoplasmic reticulum (ER). Both the ribosome and translocon are complex macromolecular machines whose structural and functional interactions are poorly understood. A new study by Pool (Pool, M.R. 2009. J. Cell Biol. 185:889-902) has now shown that the structure of the translocon is dictated by the identity of the protein being synthesized by the ribosome, thereby demonstrating that the two macromolecular machines are structurally coupled for functional purposes. The study also identifies an unexpected component in the apparent molecular linkage that connects the two machines, a discovery that shows the current view of translocon structure is oversimplified.
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Affiliation(s)
- Arthur E Johnson
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center and Department of Chemistry and Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, USA.
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634
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Xie W, Kanehara K, Sayeed A, Ng DTW. Intrinsic conformational determinants signal protein misfolding to the Hrd1/Htm1 endoplasmic reticulum-associated degradation system. Mol Biol Cell 2009; 20:3317-29. [PMID: 19458187 DOI: 10.1091/mbc.e09-03-0231] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Endoplasmic reticulum (ER) quality control mechanisms monitor the folding of nascent polypeptides of the secretory pathway. These are dynamic processes that retain folding proteins, promote the transport of conformationally mature proteins, and target misfolded proteins to ER-associated degradation (ERAD) pathways. Aided by the identification of numerous ERAD factors, late functions that include substrate extraction, ubiquitination, and degradation are fairly well described. By contrast, the mechanisms of substrate recognition remain mysterious. For some substrates, a specific N-linked glycan forms part of the recognition code but how it is read is incompletely understood. In this study, systematic analysis of model substrates revealed such glycans mark structural determinants that are sensitive to the overall folding state of the molecule. This strategy effectively generates intrinsic folding sensors that communicate with high fidelity to ERAD. Normally, these segments fold into the mature structure to pass the ERAD checkpoint. However, should a molecule fail to fold completely, they form a bipartite signal that comprises the unfolded local structure and adjacent enzymatically remodeled glycan. Only if both elements are present will the substrate be targeted to the ERAD pathway for degradation.
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Affiliation(s)
- Wei Xie
- Temasek Life Sciences Laboratory, National University of Singapore, Singapore 117604
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635
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Chakrabarti O, Ashok A, Hegde RS. Prion protein biosynthesis and its emerging role in neurodegeneration. Trends Biochem Sci 2009; 34:287-95. [PMID: 19447626 DOI: 10.1016/j.tibs.2009.03.001] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2009] [Revised: 02/23/2009] [Accepted: 03/02/2009] [Indexed: 01/03/2023]
Abstract
Various fatal neurodegenerative disorders are caused by altered metabolism of the prion protein (PrP). These diseases are typically transmissible by an unusual 'protein-only' mechanism in which a misfolded isomer, PrP(Sc), confers its aberrant conformation onto normal cellular PrP. An impressive range of studies has investigated nearly every aspect of this fascinating event; yet, our understanding of how PrP(Sc) accumulation might lead to cellular dysfunction and neurodegeneration is trifling. Recent advances in our understanding of normal PrP biosynthesis and degradation might have unexpectedly shed new light on this complex problem. Indeed, our current understanding of normal PrP cell biology, coupled with a growing appreciation of its complex metabolism, is providing new hypotheses for PrP-mediated neurodegeneration.
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Affiliation(s)
- Oishee Chakrabarti
- Cell Biology and Metabolism Program, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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636
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Cross BCS, High S. Dissecting the physiological role of selective transmembrane-segment retention at the ER translocon. J Cell Sci 2009; 122:1768-77. [PMID: 19417003 DOI: 10.1242/jcs.046094] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The membrane integration of polytopic proteins is coordinated at the endoplasmic reticulum (ER) by the conserved Sec61 translocon, which facilitates the lateral release of transmembrane (TM) segments into the lipid phase during polypeptide translocation. Here we use a site-specific crosslinking strategy to study the membrane integration of a new model protein and show that the TM segments of the P2X2 receptor are retained at the Sec61 complex for the entire duration of the biosynthetic process. This extremely prolonged association implicates the Sec61 complex in the regulation of the membrane integration process, and we use both in vitro and in vivo analyses to study this effect further. TM-segment retention depends on the association of the ribosome with the Sec61 complex, and complete lateral exit of the P2X2 TM segments was only induced by the artificial termination of translation. In the event of the premature release of P2X2 TM1 from the ER translocon, the truncated polypeptide fragment was to found aggregate in the ER membrane, suggesting a distinct physiological requirement for the delayed release of TM segments from the ER translocon site.
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Affiliation(s)
- Benedict C S Cross
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK
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637
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Kaiser E, Pust S, Kroll C, Barth H. Cyclophilin A facilitates translocation of theClostridium botulinumC2 toxin across membranes of acidified endosomes into the cytosol of mammalian cells. Cell Microbiol 2009; 11:780-95. [DOI: 10.1111/j.1462-5822.2009.01291.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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638
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An IcmF family protein, ImpLM, is an integral inner membrane protein interacting with ImpKL, and its walker a motif is required for type VI secretion system-mediated Hcp secretion in Agrobacterium tumefaciens. J Bacteriol 2009; 191:4316-29. [PMID: 19395482 DOI: 10.1128/jb.00029-09] [Citation(s) in RCA: 121] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
An intracellular multiplication F (IcmF) family protein is a conserved component of a newly identified type VI secretion system (T6SS) encoded in many animal and plant-associated Proteobacteria. We have previously identified ImpL(M), an IcmF family protein that is required for the secretion of the T6SS substrate hemolysin-coregulated protein (Hcp) from the plant-pathogenic bacterium Agrobacterium tumefaciens. In this study, we characterized the topology of ImpL(M) and the importance of its nucleotide-binding Walker A motif involved in Hcp secretion from A. tumefaciens. A combination of beta-lactamase-green fluorescent protein fusion and biochemical fractionation analyses revealed that ImpL(M) is an integral polytopic inner membrane protein comprising three transmembrane domains bordered by an N-terminal domain facing the cytoplasm and a C-terminal domain exposed to the periplasm. impL(M) mutants with substitutions or deletions in the Walker A motif failed to complement the impL(M) deletion mutant for Hcp secretion, which provided evidence that ImpL(M) may bind and/or hydrolyze nucleoside triphosphates to mediate T6SS machine assembly and/or substrate secretion. Protein-protein interaction and protein stability analyses indicated that there is a physical interaction between ImpL(M) and another essential T6SS component, ImpK(L). Topology and biochemical fractionation analyses suggested that ImpK(L) is an integral bitopic inner membrane protein with an N-terminal domain facing the cytoplasm and a C-terminal OmpA-like domain exposed to the periplasm. Further comprehensive yeast two-hybrid assays dissecting ImpL(M)-ImpK(L) interaction domains suggested that ImpL(M) interacts with ImpK(L) via the N-terminal cytoplasmic domains of the proteins. In conclusion, ImpL(M) interacts with ImpK(L), and its Walker A motif is required for its function in mediation of Hcp secretion from A. tumefaciens.
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639
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Saier MH, Ma CH, Rodgers L, Tamang DG, Yen MR. Protein secretion and membrane insertion systems in bacteria and eukaryotic organelles. ADVANCES IN APPLIED MICROBIOLOGY 2009; 65:141-97. [PMID: 19026865 DOI: 10.1016/s0065-2164(08)00606-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Milton H Saier
- Division of Biological Sciences, University of California at San Diego, La Jolla, California 92093-0116, USA
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640
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Oligosaccharyltransferase directly binds to ribosome at a location near the translocon-binding site. Proc Natl Acad Sci U S A 2009; 106:6945-9. [PMID: 19365066 DOI: 10.1073/pnas.0812489106] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Oligosaccharyltransferase (OT) transfers high mannose-type glycans to the nascent polypeptides that are translated by the membrane-bound ribosome and translocated into the lumen of the endoplasmic reticulum through the Sec61 translocon complex. In this article, we show that purified ribosomes and OT can form a binary complex with a stoichiometry of approximately 1 to 1 in the presence of detergent. We present evidence that OT may bind to the large ribosomal subunit near the site where nascent polypeptides exit. We further show that OT and the Sec61 complex can simultaneously bind to ribosomes in vitro. Based on existing data and our findings, we propose that cotranslational translocation and N-glycosylation of nascent polypeptides are mediated by a ternary supramolecular complex consisting of OT, the Sec61 complex, and ribosomes.
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641
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Enquist K, Fransson M, Boekel C, Bengtsson I, Geiger K, Lang L, Pettersson A, Johansson S, von Heijne G, Nilsson I. Membrane-integration Characteristics of Two ABC Transporters, CFTR and P-glycoprotein. J Mol Biol 2009; 387:1153-64. [DOI: 10.1016/j.jmb.2009.02.035] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2008] [Revised: 02/05/2009] [Accepted: 02/13/2009] [Indexed: 10/21/2022]
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642
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Abstract
Correct protein function depends on delivery to the appropriate cellular or subcellular compartment. Following the initiation of protein synthesis in the cytosol, many bacterial and eukaryotic proteins must be integrated into or transported across a membrane to reach their site of function. Whereas in the post-translational delivery pathway ATP-dependent factors bind to completed polypeptides and chaperone them until membrane translocation is initiated, a GTP-dependent co-translational pathway operates to couple ongoing protein synthesis to membrane transport. These distinct pathways provide different solutions for the maintenance of proteins in a state that is competent for membrane translocation and their delivery for export from the cytosol.
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643
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Dalal K, Nguyen N, Alami M, Tan J, Moraes TF, Lee WC, Maurus R, Sligar SS, Brayer GD, Duong F. Structure, binding, and activity of Syd, a SecY-interacting protein. J Biol Chem 2009; 284:7897-902. [PMID: 19139097 PMCID: PMC2658082 DOI: 10.1074/jbc.m808305200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2008] [Revised: 12/19/2008] [Indexed: 01/20/2023] Open
Abstract
The Syd protein has been implicated in the Sec-dependent transport of polypeptides across the bacterial inner membrane. Using Nanodiscs, we here provide direct evidence that Syd binds the SecY complex, and we demonstrate that interaction involves the two electropositive and cytosolic loops of the SecY subunit. We solve the crystal structure of Syd and together with cysteine cross-link analysis, we show that a conserved concave and electronegative groove constitutes the SecY-binding site. At the membrane, Syd decreases the activity of the translocon containing loosely associated SecY-SecE subunits, whereas in detergent solution Syd disrupts the SecYEG heterotrimeric associations. These results support the role of Syd in proofreading the SecY complex biogenesis and point to the electrostatic nature of the Sec channel interaction with its cytosolic partners.
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Affiliation(s)
- Kush Dalal
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia V6T1Z3, Canada
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644
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Knowles TJ, Scott-Tucker A, Overduin M, Henderson IR. Membrane protein architects: the role of the BAM complex in outer membrane protein assembly. Nat Rev Microbiol 2009; 7:206-14. [DOI: 10.1038/nrmicro2069] [Citation(s) in RCA: 231] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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645
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Haase S, Herrmann S, Grüring C, Heiber A, Jansen PW, Langer C, Treeck M, Cabrera A, Bruns C, Struck NS, Kono M, Engelberg K, Ruch U, Stunnenberg HG, Gilberger TW, Spielmann T. Sequence requirements for the export of thePlasmodium falciparumMaurer's clefts protein REX2. Mol Microbiol 2009; 71:1003-17. [DOI: 10.1111/j.1365-2958.2008.06582.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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646
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Hong H, Joh NH, Bowie JU, Tamm LK. Chapter 8 Methods for Measuring the Thermodynamic Stability of Membrane Proteins. Methods Enzymol 2009; 455:213-36. [DOI: 10.1016/s0076-6879(08)04208-0] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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647
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Abstract
Despite intense study, the role of the immune system in detecting (immunosurveillance), controlling and remodeling (immunoediting) neoplasia remains elusive. We present here a comparative view of the complex interactions between neoplasia and the host immune system. We provide evidence, in the amphibian Xenopus laevis, consistent with an evolutionarily conserved and crucial role of the immune system in controlling neoplasia, which involves a striking variety of anti-tumoral immune effectors including conventional CTLs, classical MHC class Ia unrestricted CTLs (CCU-CTLs) that interact with nonclassical MHC class Ib molecules, CD8 NKT-like cells and NK cells. We also review the tumors found in X. laevis with an emphasis on thymic lymphoid tumors and a rare ovarian dysgerminoma. Finally, we consider the use of X. laevis for in vivo study of tumorigenesis. Given our current knowledge, the experimental systems already established in X. laevis, and the rapid accumulation of genetic resources for the sister species Silurana (Xenopus) tropicalis, it is our conviction that these species provide an ideal alternative to the murine system for studying tumorigenesis and tumor immunity.
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Affiliation(s)
- Ana Goyos
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, NY 14642, USA
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648
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Kubick S, Gerrits M, Merk H, Stiege W, Erdmann VA. Chapter 2 In Vitro Synthesis of Posttranslationally Modified Membrane Proteins. CURRENT TOPICS IN MEMBRANES 2009. [DOI: 10.1016/s1063-5823(09)63002-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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649
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Endoplasmic Reticulum Stress in Neurodegeneration. PROTEIN FOLDING AND MISFOLDING: NEURODEGENERATIVE DISEASES 2008. [DOI: 10.1007/978-1-4020-9434-7_5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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650
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Montal M. Translocation of botulinum neurotoxin light chain protease by the heavy chain protein-conducting channel. Toxicon 2008; 54:565-9. [PMID: 19111565 DOI: 10.1016/j.toxicon.2008.11.018] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2008] [Accepted: 11/28/2008] [Indexed: 11/25/2022]
Abstract
Clostridial botulinum neurotoxins (BoNTs) inhibit synaptic exocytosis; intoxication requires the di-chain protein to undergo conformational changes in response to pH and redox gradients across the endosomal membrane with consequent formation of a protein-conducting channel by the heavy chain (HC) that translocates the light chain (LC) protease into the cytosol, colocalizing it with the substrate SNARE proteins. We investigate the dynamics of protein translocation across membranes using a sensitive single-molecule assay to track translocation events with millisecond resolution on lipid bilayers and on membrane patches of Neuro 2A cells. Translocation of BoNT/A LC by the HC is observed in real time as changes of channel conductance: the channel is occluded by the light chain during transit, and open after completion of translocation and release of cargo, acting intriguingly similar to the protein-conducting/translocating channels of the endoplasmic reticulum, mitochondria, and chloroplasts. Our findings support the notion of an interdependent, tight interplay between the HC transmembrane chaperone and the LC cargo that prevents LC aggregation and dictates the productive passage of cargo through the channel and completion of translocation. The protein-conducting channel of BoNT, a key element in the process of neurotoxicity, emerges therefore as a target for antidote discovery - a novel paradigm of paramount significance to health science and biodefense.
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Affiliation(s)
- Mauricio Montal
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0366, United States
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