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Su H, Shi P, Shen Z, Meng H, Meng Z, Han X, Chen Y, Fan W, Fa Y, Yang C, Li F, Wang S. High-level production of nervonic acid in the oleaginous yeast Yarrowia lipolytica by systematic metabolic engineering. Commun Biol 2023; 6:1125. [PMID: 37935958 PMCID: PMC10630375 DOI: 10.1038/s42003-023-05502-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Accepted: 10/20/2023] [Indexed: 11/09/2023] Open
Abstract
Nervonic acid benefits the treatment of neurological diseases and the health of brain. In this study, we employed the oleaginous yeast Yarrowia lipolytica to overproduce nervonic acid oil by systematic metabolic engineering. First, the production of nervonic acid was dramatically improved by iterative expression of the genes ecoding β-ketoacyl-CoA synthase CgKCS, fatty acid elongase gELOVL6 and desaturase MaOLE2. Second, the biosynthesis of both nervonic acid and lipids were further enhanced by expression of glycerol-3-phosphate acyltransferases and diacylglycerol acyltransferases from Malania oleifera in endoplasmic reticulum (ER). Third, overexpression of a newly identified ER structure regulator gene YlINO2 led to a 39.3% increase in lipid production. Fourth, disruption of the AMP-activated S/T protein kinase gene SNF1 increased the ratio of nervonic acid to lignoceric acid by 61.6%. Next, pilot-scale fermentation using the strain YLNA9 exhibited a lipid titer of 96.7 g/L and a nervonic acid titer of 17.3 g/L (17.9% of total fatty acids), the highest reported titer to date. Finally, a proof-of-concept purification and separation of nervonic acid were performed and the purity of it reached 98.7%. This study suggested that oleaginous yeasts are attractive hosts for the cost-efficient production of nervonic acid and possibly other very long-chain fatty acids (VLCFAs).
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Affiliation(s)
- Hang Su
- Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, China
- University of Chinese Academy of Sciences, Beijing, 100039, China
| | - Penghui Shi
- Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, China
- Shandong Energy Institute, Qingdao, 266101, China
| | - Zhaoshuang Shen
- Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, China
- Shandong Energy Institute, Qingdao, 266101, China
| | - Huimin Meng
- Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, China
- Qingdao Institute for Food and Drug Control, Qingdao, 266073, China
| | - Ziyue Meng
- Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, China
- University of Chinese Academy of Sciences, Beijing, 100039, China
| | - Xingfeng Han
- Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, China
| | - Yanna Chen
- Zhejiang Zhenyuan Biotech Co., LTD, Shaoxing, 312365, China
| | - Weiming Fan
- Zhejiang Zhenyuan Biotech Co., LTD, Shaoxing, 312365, China
| | - Yun Fa
- Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, China
- Shandong Energy Institute, Qingdao, 266101, China
- Qingdao New Energy Shandong Laboratory, Qingdao, 266101, China
| | - Chunyu Yang
- State Key Laboratory of Microbial Technology, Institute of Microbial Technology, Shandong University, Qingdao, 266237, China
| | - Fuli Li
- Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, China.
- Shandong Energy Institute, Qingdao, 266101, China.
- Qingdao New Energy Shandong Laboratory, Qingdao, 266101, China.
| | - Shi'an Wang
- Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, China.
- Shandong Energy Institute, Qingdao, 266101, China.
- Qingdao New Energy Shandong Laboratory, Qingdao, 266101, China.
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Levray YS, Bana B, Tarr SJ, McLaughlin EJ, Rossi-Smith P, Waltho A, Charlton GH, Chiozzi RZ, Straton CR, Thalassinos K, Osborne AR. Formation of ER-lumenal intermediates during export of Plasmodium proteins containing transmembrane-like hydrophobic sequences. PLoS Pathog 2023; 19:e1011281. [PMID: 37000891 PMCID: PMC10096305 DOI: 10.1371/journal.ppat.1011281] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Revised: 04/12/2023] [Accepted: 03/08/2023] [Indexed: 04/03/2023] Open
Abstract
During the blood stage of a malaria infection, malaria parasites export both soluble and membrane proteins into the erythrocytes in which they reside. Exported proteins are trafficked via the parasite endoplasmic reticulum and secretory pathway, before being exported across the parasitophorous vacuole membrane into the erythrocyte. Transport across the parasitophorous vacuole membrane requires protein unfolding, and in the case of membrane proteins, extraction from the parasite plasma membrane. We show that trafficking of the exported Plasmodium protein, Pf332, differs from that of canonical eukaryotic soluble-secreted and transmembrane proteins. Pf332 is initially ER-targeted by an internal hydrophobic sequence that unlike a signal peptide, is not proteolytically removed, and unlike a transmembrane segment, does not span the ER membrane. Rather, both termini of the hydrophobic sequence enter the ER-lumen and the ER-lumenal species is a productive intermediate for protein export. Furthermore, we show in intact cells, that two other exported membrane proteins, SBP1 and MAHRP2, assume a lumenal topology within the parasite secretory pathway. Although the addition of a C-terminal ER-retention sequence, recognised by the lumenal domain of the KDEL receptor, does not completely block export of SBP1 and MAHRP2, it does enhance their retention in the parasite ER. This indicates that a sub-population of each protein adopts an ER-lumenal state that is an intermediate in the export process. Overall, this suggests that although many exported proteins traverse the parasite secretory pathway as typical soluble or membrane proteins, some exported proteins that are ER-targeted by a transmembrane segment-like, internal, non-cleaved hydrophobic segment, do not integrate into the ER membrane, and form an ER-lumenal species that is a productive export intermediate. This represents a novel means, not seen in typical membrane proteins found in model systems, by which exported transmembrane-like proteins can be targeted and trafficked within the lumen of the secretory pathway.
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Efficient integration of transmembrane domains depends on the folding properties of the upstream sequences. Proc Natl Acad Sci U S A 2021; 118:2102675118. [PMID: 34373330 PMCID: PMC8379923 DOI: 10.1073/pnas.2102675118] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The topology of membrane proteins is defined by the successive integration of α-helical transmembrane domains at the Sec61 translocon. For each polypeptide segment of ∼20 residues entering the translocon, their combined hydrophobicities were previously shown to define membrane integration. Here, we discovered that different sequences preceding a potential transmembrane domain substantially affect the hydrophobicity threshold. Sequences that are rapidly folding, intrinsically disordered, very short, or strongly binding chaperones allow efficient integration at low hydrophobicity. Folding deficient mutant domains and artificial sequences not binding chaperones interfered with membrane integration likely by remaining partially unfolded and exposing hydrophobic surfaces that compete with the translocon for the emerging transmembrane segment, reducing integration efficiency. Rapid folding or strong chaperone binding thus promote efficient integration. The topology of most membrane proteins is defined by the successive integration of α-helical transmembrane domains at the Sec61 translocon. The translocon provides a pore for the transfer of polypeptide segments across the membrane while giving them lateral access to the lipid. For each polypeptide segment of ∼20 residues, the combined hydrophobicities of its constituent amino acids were previously shown to define the extent of membrane integration. Here, we discovered that different sequences preceding a potential transmembrane domain substantially affect its hydrophobicity requirement for integration. Rapidly folding domains, sequences that are intrinsically disordered or very short or capable of binding chaperones with high affinity, allow for efficient transmembrane integration with low-hydrophobicity thresholds for both orientations in the membrane. In contrast, long protein fragments, folding-deficient mutant domains, and artificial sequences not binding chaperones interfered with membrane integration, requiring higher hydrophobicity. We propose that the latter sequences, as they compact on their hydrophobic residues, partially folded but unable to reach a native state, expose hydrophobic surfaces that compete with the translocon for the emerging transmembrane segment, reducing integration efficiency. The results suggest that rapid folding or strong chaperone binding is required for efficient transmembrane integration.
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Ito K, Shimokawa-Chiba N, Chiba S. Sec translocon has an insertase-like function in addition to polypeptide conduction through the channel. F1000Res 2020; 8. [PMID: 32025287 PMCID: PMC6971846 DOI: 10.12688/f1000research.21065.1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 12/17/2019] [Indexed: 11/20/2022] Open
Abstract
The Sec translocon provides a polypeptide-conducting channel, which is insulated from the hydrophobic lipidic environment of the membrane, for translocation of hydrophilic passenger polypeptides. Its lateral gate allows a downstream hydrophobic segment (stop-transfer sequence) to exit the channel laterally for integration into the lipid phase. We note that this channel model only partly accounts for the translocon function. The other essential role of translocon is to facilitate de novo insertion of the N-terminal topogenic segment of a substrate polypeptide into the membrane. Recent structural studies suggest that de novo insertion does not use the polypeptide-conducting channel; instead, it takes place directly at the lateral gate, which is prone to opening. We propose that the de novo insertion process, in concept, is similar to that of insertases (such as YidC in bacteria and EMC3 in eukaryotes), in which an intramembrane surface of the machinery provides the halfway point of insertion.
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Affiliation(s)
- Koreaki Ito
- Faculty of Life Sciences and Institute for Protein Dynamics, Kyoto Sangyo University, Kyoto, Japan
| | - Naomi Shimokawa-Chiba
- Faculty of Life Sciences and Institute for Protein Dynamics, Kyoto Sangyo University, Kyoto, Japan
| | - Shinobu Chiba
- Faculty of Life Sciences and Institute for Protein Dynamics, Kyoto Sangyo University, Kyoto, Japan
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Abstract
A subset of membrane proteins is targeted to and inserted into the membrane via a hydrophobic transmembrane domain (TMD) that is positioned at the very C terminus of the protein. The biogenesis of these so-called tail-anchored proteins (TAMPs) has been studied in detail in eukaryotic cells. Various partly redundant pathways were identified, the choice for which depends in part on the hydrophobicity of the TMD. Much less is known about bacterial TAMPs. The significance of our research is in identifying the role of TMD hydrophobicity in the routing of E. coli TAMPs. Our data suggest that both the nature of the TMD and its role in routing can be very different for TAMPs versus “regular” membrane proteins. Elucidating these position-specific effects of TMDs will increase our understanding of how prokaryotic cells face the challenge of producing a wide variety of membrane proteins. Tail-anchored membrane proteins (TAMPs) are a distinct subset of inner membrane proteins (IMPs) characterized by a single C-terminal transmembrane domain (TMD) that is responsible for both targeting and anchoring. Little is known about the routing of TAMPs in bacteria. Here, we have investigated the role of TMD hydrophobicity in tail-anchor function in Escherichia coli and its influence on the choice of targeting/insertion pathway. We created a set of synthetic, fluorescent TAMPs that vary in the hydrophobicity of their TMDs and corresponding control polypeptides that are extended at their C terminus to create regular type II IMPs. Surprisingly, we observed that TAMPs have a much lower TMD hydrophobicity threshold for efficient targeting and membrane insertion than their type II counterparts. Using strains conditional for the expression of known membrane-targeting and insertion factors, we show that TAMPs with strongly hydrophobic TMDs require the signal recognition particle (SRP) for targeting. Neither the SecYEG translocon nor YidC appears to be essential for the membrane insertion of any of the TAMPs studied. In contrast, corresponding type II IMPs with a TMD of sufficient hydrophobicity to promote membrane insertion followed an SRP- and SecYEG translocon-dependent pathway. Together, these data indicate that the capacity of a TMD to promote the biogenesis of E. coli IMPs is strongly dependent upon the polypeptide context in which it is presented.
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Spiess M, Junne T, Janoschke M. Membrane Protein Integration and Topogenesis at the ER. Protein J 2019; 38:306-316. [DOI: 10.1007/s10930-019-09827-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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Krampen L, Malmsheimer S, Grin I, Trunk T, Lührmann A, de Gier JW, Wagner S. Revealing the mechanisms of membrane protein export by virulence-associated bacterial secretion systems. Nat Commun 2018; 9:3467. [PMID: 30150748 PMCID: PMC6110835 DOI: 10.1038/s41467-018-05969-w] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 07/31/2018] [Indexed: 02/08/2023] Open
Abstract
Many bacteria export effector proteins fulfilling their function in membranes of a eukaryotic host. These effector membrane proteins appear to contain signals for two incompatible bacterial secretion pathways in the same protein: a specific export signal, as well as transmembrane segments that one would expect to mediate targeting to the bacterial inner membrane. Here, we show that the transmembrane segments of effector proteins of type III and type IV secretion systems indeed integrate in the membrane as required in the eukaryotic host, but that their hydrophobicity in most instances is just below the threshold required for mediating targeting to the bacterial inner membrane. Furthermore, we show that binding of type III secretion chaperones to both the effector’s chaperone-binding domain and adjacent hydrophobic transmembrane segments also prevents erroneous targeting. These results highlight the evolution of a fine discrimination between targeting pathways that is critical for the virulence of many bacterial pathogens. Many bacteria export effector proteins even when two incompatible signal sequences are present, one which would lead to export and the other to inner membrane targeting. Here the authors show that such proteins feature decreased hydrophobicity or cognate chaperone binding to prevent erroneous targeting.
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Affiliation(s)
- Lea Krampen
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany
| | - Silke Malmsheimer
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany
| | - Iwan Grin
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany
| | - Thomas Trunk
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany.,Section for Genetics and Evolutionary Biology, University of Oslo, Blindernveien 31, 0371, Oslo, Norway
| | - Anja Lührmann
- Institute of Microbiology, University Hospital Erlangen, Wasserturmstr. 3-5, 91054, Erlangen, Germany
| | - Jan-Willem de Gier
- Center for Biomembrane Research, Stockholm University, Svante-Arrhenius väg 16, SE-106 91, Stockholm, Sweden
| | - Samuel Wagner
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany. .,German Center for Infection Research (DZIF), Partner-site Tübingen, Elfriede-Aulhorn-Str. 6, 72076, Tübingen, Germany.
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Baker JA, Wong WC, Eisenhaber B, Warwicker J, Eisenhaber F. Charged residues next to transmembrane regions revisited: "Positive-inside rule" is complemented by the "negative inside depletion/outside enrichment rule". BMC Biol 2017; 15:66. [PMID: 28738801 PMCID: PMC5525207 DOI: 10.1186/s12915-017-0404-4] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Accepted: 07/07/2017] [Indexed: 11/25/2022] Open
Abstract
Background Transmembrane helices (TMHs) frequently occur amongst protein architectures as means for proteins to attach to or embed into biological membranes. Physical constraints such as the membrane’s hydrophobicity and electrostatic potential apply uniform requirements to TMHs and their flanking regions; consequently, they are mirrored in their sequence patterns (in addition to TMHs being a span of generally hydrophobic residues) on top of variations enforced by the specific protein’s biological functions. Results With statistics derived from a large body of protein sequences, we demonstrate that, in addition to the positive charge preference at the cytoplasmic inside (positive-inside rule), negatively charged residues preferentially occur or are even enriched at the non-cytoplasmic flank or, at least, they are suppressed at the cytoplasmic flank (negative-not-inside/negative-outside (NNI/NO) rule). As negative residues are generally rare within or near TMHs, the statistical significance is sensitive with regard to details of TMH alignment and residue frequency normalisation and also to dataset size; therefore, this trend was obscured in previous work. We observe variations amongst taxa as well as for organelles along the secretory pathway. The effect is most pronounced for TMHs from single-pass transmembrane (bitopic) proteins compared to those with multiple TMHs (polytopic proteins) and especially for the class of simple TMHs that evolved for the sole role as membrane anchors. Conclusions The charged-residue flank bias is only one of the TMH sequence features with a role in the anchorage mechanisms, others apparently being the leucine intra-helix propensity skew towards the cytoplasmic side, tryptophan flanking as well as the cysteine and tyrosine inside preference. These observations will stimulate new prediction methods for TMHs and protein topology from a sequence as well as new engineering designs for artificial membrane proteins. Electronic supplementary material The online version of this article (doi:10.1186/s12915-017-0404-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- James Alexander Baker
- Bioinformatics Institute, Agency for Science Technology and Research (A*STAR), 30 Biopolis Street #07-01, Matrix, Singapore, 138671, Singapore.,School of Chemistry, Manchester Institute of Biotechnology, 131 Princess Street, Manchester, M1 7DN, UK
| | - Wing-Cheong Wong
- Bioinformatics Institute, Agency for Science Technology and Research (A*STAR), 30 Biopolis Street #07-01, Matrix, Singapore, 138671, Singapore
| | - Birgit Eisenhaber
- Bioinformatics Institute, Agency for Science Technology and Research (A*STAR), 30 Biopolis Street #07-01, Matrix, Singapore, 138671, Singapore
| | - Jim Warwicker
- School of Chemistry, Manchester Institute of Biotechnology, 131 Princess Street, Manchester, M1 7DN, UK.
| | - Frank Eisenhaber
- Bioinformatics Institute, Agency for Science Technology and Research (A*STAR), 30 Biopolis Street #07-01, Matrix, Singapore, 138671, Singapore. .,School of Computer Engineering (SCE), Nanyang Technological University (NTU), 50 Nanyang Drive, Singapore, 637553, Singapore.
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Tooke FJ, Babot M, Chandra G, Buchanan G, Palmer T. A unifying mechanism for the biogenesis of membrane proteins co-operatively integrated by the Sec and Tat pathways. eLife 2017; 6. [PMID: 28513434 PMCID: PMC5449189 DOI: 10.7554/elife.26577] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Accepted: 05/15/2017] [Indexed: 11/13/2022] Open
Abstract
The majority of multi-spanning membrane proteins are co-translationally inserted into the bilayer by the Sec pathway. An important subset of membrane proteins have globular, cofactor-containing extracytoplasmic domains requiring the dual action of the co-translational Sec and post-translational Tat pathways for integration. Here, we identify further unexplored families of membrane proteins that are dual Sec-Tat-targeted. We establish that a predicted heme-molybdenum cofactor-containing protein, and a complex polyferredoxin, each require the concerted action of two translocases for their assembly. We determine that the mechanism of handover from Sec to Tat pathway requires the relatively low hydrophobicity of the Tat-dependent transmembrane domain. This, coupled with the presence of C-terminal positive charges, results in abortive insertion of this transmembrane domain by the Sec pathway and its subsequent release at the cytoplasmic side of the membrane. Together, our data points to a simple unifying mechanism governing the assembly of dual targeted membrane proteins.
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Affiliation(s)
- Fiona J Tooke
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Marion Babot
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Govind Chandra
- Department of Molecular Microbiology, John Innes Centre, Norwich, United Kingdom
| | - Grant Buchanan
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Tracy Palmer
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
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Abstract
The insertion and assembly of proteins into the inner membrane of bacteria are crucial for many cellular processes, including cellular respiration, signal transduction, and ion and pH homeostasis. This process requires efficient membrane targeting and insertion of proteins into the lipid bilayer in their correct orientation and proper conformation. Playing center stage in these events are the targeting components, signal recognition particle (SRP) and the SRP receptor FtsY, as well as the insertion components, the Sec translocon and the YidC insertase. Here, we will discuss new insights provided from the recent high-resolution structures of these proteins. In addition, we will review the mechanism by which a variety of proteins with different topologies are inserted into the inner membrane of Gram-negative bacteria. Finally, we report on the energetics of this process and provide information on how membrane insertion occurs in Gram-positive bacteria and Archaea. It should be noted that most of what we know about membrane protein assembly in bacteria is based on studies conducted in Escherichia coli.
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Affiliation(s)
- Andreas Kuhn
- Institute for Microbiology and Molecular Biology, University of Hohenheim, 70599 Stuttgart, Germany
| | - Hans-Georg Koch
- Institute for Biochemistry and Molecular Biology, Faculty of Medicine, Albert-Ludwigs-University of Freiburg, 79104, Freiburg, Germany
| | - Ross E Dalbey
- Department of Chemistry, The Ohio State University, Columbus, OH 43210
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11
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Interplay between hydrophobicity and the positive-inside rule in determining membrane-protein topology. Proc Natl Acad Sci U S A 2016; 113:10340-5. [PMID: 27562165 DOI: 10.1073/pnas.1605888113] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The energetics of membrane-protein interactions determine protein topology and structure: hydrophobicity drives the insertion of helical segments into the membrane, and positive charges orient the protein with respect to the membrane plane according to the positive-inside rule. Until recently, however, quantifying these contributions met with difficulty, precluding systematic analysis of the energetic basis for membrane-protein topology. We recently developed the dsTβL method, which uses deep sequencing and in vitro selection of segments inserted into the bacterial plasma membrane to infer insertion-energy profiles for each amino acid residue across the membrane, and quantified the insertion contribution from hydrophobicity and the positive-inside rule. Here, we present a topology-prediction algorithm called TopGraph, which is based on a sequence search for minimum dsTβL insertion energy. Whereas the average insertion energy assigned by previous experimental scales was positive (unfavorable), the average assigned by TopGraph in a nonredundant set is -6.9 kcal/mol. By quantifying contributions from both hydrophobicity and the positive-inside rule we further find that in about half of large membrane proteins polar segments are inserted into the membrane to position more positive charges in the cytoplasm, suggesting an interplay between these two energy contributions. Because membrane-embedded polar residues are crucial for substrate binding and conformational change, the results implicate the positive-inside rule in determining the architectures of membrane-protein functional sites. This insight may aid structure prediction, engineering, and design of membrane proteins. TopGraph is available online (topgraph.weizmann.ac.il).
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Gumbart JC, Chipot C. Decrypting protein insertion through the translocon with free-energy calculations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:1663-71. [PMID: 26896694 DOI: 10.1016/j.bbamem.2016.02.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Revised: 02/11/2016] [Accepted: 02/12/2016] [Indexed: 12/23/2022]
Abstract
Protein insertion into a membrane is a complex process involving numerous players. The most prominent of these players is the Sec translocon complex, a conserved protein-conducting channel present in the cytoplasmic membrane of bacteria and the membrane of the endoplasmic reticulum in eukaryotes. The last decade has seen tremendous leaps forward in our understanding of how insertion is managed by the translocon and its partners, coming from atomic-detailed structures, innovative experiments, and well-designed simulations. In this review, we discuss how experiments and simulations, hand-in-hand, teased out the secrets of the translocon-facilitated membrane insertion process. In particular, we focus on the role of free-energy calculations in elucidating membrane insertion. Amazingly, despite all its apparent complexity, protein insertion into membranes is primarily driven by simple thermodynamic and kinetic principles. This article is part of a Special Issue entitled: Membrane proteins edited by J.C. Gumbart and Sergei Noskov.
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Affiliation(s)
- James C Gumbart
- School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA.
| | - Christophe Chipot
- Laboratoire International Associé Centre National de la Recherche Scientifique and University of Illinois at Urbana-Champaign, UMR n° 7565, Université de Lorraine, B.P. 70239, 54506 Vandœuvre-lès-Nancy, France; Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
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13
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Gan Q, Dai J, Zhou HX, Wollmuth LP. The Transmembrane Domain Mediates Tetramerization of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors. J Biol Chem 2016; 291:6595-606. [PMID: 26839312 DOI: 10.1074/jbc.m115.686246] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Indexed: 11/06/2022] Open
Abstract
AMPA receptors (AMPARs) mediate fast excitatory neurotransmission in the central nervous system. Functional AMPARs are tetrameric complexes with a highly modular structure, consisting of four evolutionarily distinct structural domains: an amino-terminal domain (ATD), a ligand-binding domain (LBD), a channel-forming transmembrane domain (TMD), and a carboxyl-terminal domain (CTD). Here we show that the isolated TMD of the GluA1 AMPAR is fully capable of tetramerization. Additionally, removal of the extracellular domains from the receptor did not affect membrane topology or surface delivery. Furthermore, whereas the ATD and CTD contribute positively to tetramerization, the LBD presents a barrier to the process by reducing the stability of the receptor complex. These experiments pinpoint the TMD as the "tetramerization domain" for AMPARs, with other domains playing modulatory roles. They also raise intriguing questions about the evolution of iGluRs as well as the mechanisms regulating the biogenesis of AMPAR complexes.
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Affiliation(s)
- Quan Gan
- Graduate Program in Neuroscience, From the Department of Neurobiology and Behavior
| | - Jian Dai
- the Department of Physics and Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306
| | - Huan-Xiang Zhou
- the Department of Physics and Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306
| | - Lonnie P Wollmuth
- From the Department of Neurobiology and Behavior, the Department of Biochemistry and Cell Biology, and the Center for Nervous System Disorders, Stony Brook University, Stony Brook, New York 11794-5230 and
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Elazar A, Weinstein J, Biran I, Fridman Y, Bibi E, Fleishman SJ. Mutational scanning reveals the determinants of protein insertion and association energetics in the plasma membrane. eLife 2016; 5:e12125. [PMID: 26824389 PMCID: PMC4786438 DOI: 10.7554/elife.12125] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2015] [Accepted: 01/28/2016] [Indexed: 11/13/2022] Open
Abstract
Insertion of helix-forming segments into the membrane and their association determines the structure, function, and expression levels of all plasma membrane proteins. However, systematic and reliable quantification of membrane-protein energetics has been challenging. We developed a deep mutational scanning method to monitor the effects of hundreds of point mutations on helix insertion and self-association within the bacterial inner membrane. The assay quantifies insertion energetics for all natural amino acids at 27 positions across the membrane, revealing that the hydrophobicity of biological membranes is significantly higher than appreciated. We further quantitate the contributions to membrane-protein insertion from positively charged residues at the cytoplasm-membrane interface and reveal large and unanticipated differences among these residues. Finally, we derive comprehensive mutational landscapes in the membrane domains of Glycophorin A and the ErbB2 oncogene, and find that insertion and self-association are strongly coupled in receptor homodimers.
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Affiliation(s)
- Assaf Elazar
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Jonathan Weinstein
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Ido Biran
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Yearit Fridman
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Eitan Bibi
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
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15
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Junne T, Spiess M. Integration of transmembrane domains is regulated by their downstream sequences. J Cell Sci 2016; 130:372-381. [DOI: 10.1242/jcs.194472] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 11/10/2016] [Indexed: 12/31/2022] Open
Abstract
The Sec61 translocon catalyzes translocation of proteins into the endoplasmic reticulum and the lateral integration of transmembrane segments into the lipid bilayer. Integration is mediated by the hydrophobicity of a polypeptide segment consistent with thermodynamic equilibration between the translocon and the lipid membrane. Integration efficiency of a generic series of increasingly hydrophobic sequences (H-segments) was found to diverge significantly in different reporter constructs as a function of the ∼100 residues carboxyterminal of the H-segments. The hydrophobicity threshold of integration was considerably lowered by insertion of generic ∼20-residue peptides either made of flexible glycine-serine repeats, containing multiple negative charges, or consisting of an oligo-proline stretch. A highly flexible, 100-residue glycine-serine stretch maximally enhanced this effect. The apparent free energy of integration was found to be changed by more than 3 kcal/mol with the downstream sequences tested. The C-terminal sequences could also be shown to affect integration of natural mildly hydrophobic sequences. The results suggest that the conformation of the nascent polypeptide in the protected cavity between ribosome and translocon significantly influences the release of the H-segment into the bilayer.
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Affiliation(s)
- Tina Junne
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
| | - Martin Spiess
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
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16
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De Marothy MT, Elofsson A. Marginally hydrophobic transmembrane α-helices shaping membrane protein folding. Protein Sci 2015; 24:1057-74. [PMID: 25970811 DOI: 10.1002/pro.2698] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 04/24/2015] [Indexed: 01/12/2023]
Abstract
Cells have developed an incredible machinery to facilitate the insertion of membrane proteins into the membrane. While we have a fairly good understanding of the mechanism and determinants of membrane integration, more data is needed to understand the insertion of membrane proteins with more complex insertion and folding pathways. This review will focus on marginally hydrophobic transmembrane helices and their influence on membrane protein folding. These weakly hydrophobic transmembrane segments are by themselves not recognized by the translocon and therefore rely on local sequence context for membrane integration. How can such segments reside within the membrane? We will discuss this in the light of features found in the protein itself as well as the environment it resides in. Several characteristics in proteins have been described to influence the insertion of marginally hydrophobic helices. Additionally, the influence of biological membranes is significant. To begin with, the actual cost for having polar groups within the membrane may not be as high as expected; the presence of proteins in the membrane as well as characteristics of some amino acids may enable a transmembrane helix to harbor a charged residue. The lipid environment has also been shown to directly influence the topology as well as membrane boundaries of transmembrane helices-implying a dynamic relationship between membrane proteins and their environment.
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Affiliation(s)
- Minttu T De Marothy
- Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University, Solna, SE-171 21, Sweden
| | - Arne Elofsson
- Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University, Solna, SE-171 21, Sweden
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17
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Götzke H, Muheim C, Altelaar AFM, Heck AJR, Maddalo G, Daley DO. Identification of putative substrates for the periplasmic chaperone YfgM in Escherichia coli using quantitative proteomics. Mol Cell Proteomics 2014; 14:216-26. [PMID: 25403562 DOI: 10.1074/mcp.m114.043216] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
How proteins are trafficked, folded, and assembled into functional units in the cell envelope of Gram-negative bacteria is of significant interest. A number of chaperones have been identified, however, the molecular roles of these chaperones are often enigmatic because it has been challenging to assign substrates. Recently we discovered a novel periplasmic chaperone, called YfgM, which associates with PpiD and the SecYEG translocon and operates in a network that contains Skp and SurA. The aim of the study presented here was to identify putative substrates of YfgM. We reasoned that substrates would be incorrectly folded or trafficked when YfgM was absent from the cell, and thus more prone to proteolysis (the loss-of-function rationale). We therefore used a comparative proteomic approach to identify cell envelope proteins that were lower in abundance in a strain lacking yfgM, and strains lacking yfgM together with either skp or surA. Sixteen putative substrates were identified. The list contained nine inner membrane proteins (CusS, EvgS, MalF, OsmC, TdcB, TdcC, WrbA, YfhB, and YtfH) and seven periplasmic proteins (HdeA, HdeB, AnsB, Ggt, MalE, YcgK, and YnjE), but it did not include any lipoproteins or outer membrane proteins. Significantly, AnsB (an asparaginase) and HdeB (a protein involved in the acid stress response), were lower in abundance in all three strains lacking yfgM. For both genes, we ruled out the possibility that they were transcriptionally down-regulated, so it is highly likely that the corresponding proteins are misfolded/mistargeted and turned-over in the absence of YfgM. For HdeB we validated this conclusion in a pulse-chase experiment. The identification of HdeB and other cell envelope proteins as potential substrates will be a valuable resource for follow-up experiments that aim to delineate molecular the function of YfgM.
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Affiliation(s)
- Hansjörg Götzke
- From the ‡Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - Claudio Muheim
- From the ‡Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - A F Maarten Altelaar
- §Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands; ¶ Netherlands Proteomics Centre, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Albert J R Heck
- §Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands; ¶ Netherlands Proteomics Centre, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Gianluca Maddalo
- From the ‡Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden; §Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands; ¶ Netherlands Proteomics Centre, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Daniel O Daley
- From the ‡Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden;
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18
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Cymer F, von Heijne G, White SH. Mechanisms of integral membrane protein insertion and folding. J Mol Biol 2014; 427:999-1022. [PMID: 25277655 DOI: 10.1016/j.jmb.2014.09.014] [Citation(s) in RCA: 243] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2014] [Revised: 09/13/2014] [Accepted: 09/22/2014] [Indexed: 11/30/2022]
Abstract
The biogenesis, folding, and structure of α-helical membrane proteins (MPs) are important to understand because they underlie virtually all physiological processes in cells including key metabolic pathways, such as the respiratory chain and the photosystems, as well as the transport of solutes and signals across membranes. Nearly all MPs require translocons--often referred to as protein-conducting channels--for proper insertion into their target membrane. Remarkable progress toward understanding the structure and functioning of translocons has been made during the past decade. Here, we review and assess this progress critically. All available evidence indicates that MPs are equilibrium structures that achieve their final structural states by folding along thermodynamically controlled pathways. The main challenge for cells is the targeting and membrane insertion of highly hydrophobic amino acid sequences. Targeting and insertion are managed in cells principally by interactions between ribosomes and membrane-embedded translocons. Our review examines the biophysical and biological boundaries of MP insertion and the folding of polytopic MPs in vivo. A theme of the review is the under-appreciated role of basic thermodynamic principles in MP folding and assembly. Thermodynamics not only dictates the final folded structure but also is the driving force for the evolution of the ribosome-translocon system of assembly. We conclude the review with a perspective suggesting a new view of translocon-guided MP insertion.
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Affiliation(s)
- Florian Cymer
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm
| | - Gunnar von Heijne
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm.,Science for Life Laboratory Stockholm University, Box 1031, SE-171 21 Solna, Sweden
| | - Stephen H White
- Department of Physiology and Biophysics and the Center for Biomembrane Systems University of California, Irvine Irvine, CA 92697
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19
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Khadria AS, Mueller BK, Stefely JA, Tan CH, Pagliarini DJ, Senes A. A Gly-zipper motif mediates homodimerization of the transmembrane domain of the mitochondrial kinase ADCK3. J Am Chem Soc 2014; 136:14068-77. [PMID: 25216398 PMCID: PMC4195374 DOI: 10.1021/ja505017f] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Interactions between α-helices within the hydrophobic environment of lipid bilayers are integral to the folding and function of transmembrane proteins; however, the major forces that mediate these interactions remain debated, and our ability to predict these interactions is still largely untested. We recently demonstrated that the frequent transmembrane association motif GASright, the GxxxG-containing fold of the glycophorin A dimer, is optimal for the formation of extended networks of Cα-H hydrogen bonds, supporting the hypothesis that these bonds are major contributors to association. We also found that optimization of Cα-H hydrogen bonding and interhelical packing is sufficient to computationally predict the structure of known GASright dimers at near atomic level. Here, we demonstrate that this computational method can be used to characterize the structure of a protein not previously known to dimerize, by predicting and validating the transmembrane dimer of ADCK3, a mitochondrial kinase. ADCK3 is involved in the biosynthesis of the redox active lipid, ubiquinone, and human ADCK3 mutations cause a cerebellar ataxia associated with ubiquinone deficiency, but the biochemical functions of ADCK3 remain largely undefined. Our experimental analyses show that the transmembrane helix of ADCK3 oligomerizes, with an interface based on an extended Gly-zipper motif, as predicted by our models. The data provide strong evidence for the hypothesis that optimization of Cα-H hydrogen bonding is an important factor in the association of transmembrane helices. This work also provides a structural foundation for investigating the role of transmembrane association in regulating the biological activity of ADCK3.
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Affiliation(s)
- Ambalika S Khadria
- Department of Biochemistry, University of Wisconsin-Madison , 433 Babcock Drive, Madison, Wisconsin 53706, United States
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20
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Wang J, Rath A, Deber CM. Functional response of the small multidrug resistance protein EmrE to mutations in transmembrane helix 2. FEBS Lett 2014; 588:3720-5. [PMID: 25157436 DOI: 10.1016/j.febslet.2014.08.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 08/12/2014] [Accepted: 08/15/2014] [Indexed: 11/19/2022]
Abstract
Escherichia coli EmrE is a small multidrug resistance protein encompassing four transmembrane (TM) sequences that oligomerizes to confer resistance to antimicrobials. Here we examined the effects on in vivo protein accumulation and ethidium resistance activity of single residue substitutions at conserved and variable positions in EmrE transmembrane segment 2 (TM2). We found that activity was reduced when conserved residues localized to one TM2 surface were replaced. Our findings suggest that conserved TM2 positions tolerate greater residue diversity than conserved sites in other EmrE TM sequences, potentially reflecting a source of substrate polyspecificity.
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Affiliation(s)
- Jun Wang
- Division of Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada; Department of Biochemistry, University of Toronto, Toronto, Ontario M5G 1A8, Canada
| | - Arianna Rath
- Division of Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada
| | - Charles M Deber
- Division of Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada; Department of Biochemistry, University of Toronto, Toronto, Ontario M5G 1A8, Canada.
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21
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Visualization of a polytopic membrane protein during SecY-mediated membrane insertion. Nat Commun 2014; 5:4103. [PMID: 24912953 DOI: 10.1038/ncomms5103] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Accepted: 05/13/2014] [Indexed: 01/16/2023] Open
Abstract
The biogenesis of polytopic membrane proteins occurs co-translationally on ribosomes that are tightly bound to a membrane-embedded protein-conducting channel: the Sec-complex. The path that is followed by nascent proteins inside the ribosome and the Sec-complex is relatively well established; however, it is not clear what the fate of the N-terminal transmembrane domains (TMDs) of polytopic membrane proteins is when the C-terminal TMDs domains are not yet synthesized. Here, we present the sub-nanometer cryo-electron microscopy structure of an in vivo generated ribosome-SecY complex that carries a membrane insertion intermediate of proteorhodopsin (PR). The structure reveals a pre-opened Sec-complex and the first two TMDs of PR already outside the SecY complex directly in front of its proposed lateral gate. Thus, our structure is in agreement with positioning of N-terminal TMDs at the periphery of SecY, and in addition, it provides clues for the molecular mechanism underlying membrane protein topogenesis.
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Denks K, Vogt A, Sachelaru I, Petriman NA, Kudva R, Koch HG. The Sec translocon mediated protein transport in prokaryotes and eukaryotes. Mol Membr Biol 2014; 31:58-84. [DOI: 10.3109/09687688.2014.907455] [Citation(s) in RCA: 123] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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23
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Bacterial-based membrane protein production. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1843:1739-49. [PMID: 24200679 DOI: 10.1016/j.bbamcr.2013.10.023] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2013] [Revised: 10/20/2013] [Accepted: 10/29/2013] [Indexed: 01/08/2023]
Abstract
Escherichia coli is by far the most widely used bacterial host for the production of membrane proteins. Usually, different strains, culture conditions and production regimes are screened for to design the optimal production process. However, these E. coli-based screening approaches often do not result in satisfactory membrane protein production yields. Recently, it has been shown that (i) E. coli strains with strongly improved membrane protein production characteristics can be engineered or selected for, (ii) many membrane proteins can be efficiently produced in E. coli-based cell-free systems, (iii) bacteria other than E. coli can be used for the efficient production of membrane proteins, and, (iv) membrane protein variants that retain functionality but are produced at higher yields than the wild-type protein can be engineered or selected for. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.
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