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Fessl T, Watkins D, Oatley P, Allen WJ, Corey RA, Horne J, Baldwin SA, Radford SE, Collinson I, Tuma R. Dynamic action of the Sec machinery during initiation, protein translocation and termination. eLife 2018; 7:35112. [PMID: 29877797 PMCID: PMC6021171 DOI: 10.7554/elife.35112] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Accepted: 06/05/2018] [Indexed: 11/13/2022] Open
Abstract
Protein translocation across cell membranes is a ubiquitous process required for protein secretion and membrane protein insertion. In bacteria, this is mostly mediated by the conserved SecYEG complex, driven through rounds of ATP hydrolysis by the cytoplasmic SecA, and the trans-membrane proton motive force. We have used single molecule techniques to explore SecY pore dynamics on multiple timescales in order to dissect the complex reaction pathway. The results show that SecA, both the signal sequence and mature components of the pre-protein, and ATP hydrolysis each have important and specific roles in channel unlocking, opening and priming for transport. After channel opening, translocation proceeds in two phases: a slow phase independent of substrate length, and a length-dependent transport phase with an intrinsic translocation rate of ~40 amino acids per second for the proOmpA substrate. Broad translocation rate distributions reflect the stochastic nature of polypeptide transport.
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Affiliation(s)
- Tomas Fessl
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom.,Faculty of Science, University of South Bohemia, Ceske Budejovice, Czech Republic
| | - Daniel Watkins
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | - Peter Oatley
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | | | - Robin Adam Corey
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | - Jim Horne
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Steve A Baldwin
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Sheena E Radford
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Ian Collinson
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | - Roman Tuma
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.,School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom.,Faculty of Science, University of South Bohemia, Ceske Budejovice, Czech Republic
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Müller M, Koch HG, Beck K, Schäfer U. Protein traffic in bacteria: multiple routes from the ribosome to and across the membrane. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 2001; 66:107-57. [PMID: 11051763 DOI: 10.1016/s0079-6603(00)66028-2] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Bacteria use several routes to target their exported proteins to the plasma membrane. The majority are exported through pores formed by SecY and SecE. Two different molecular machineries are used to target proteins to the SecYE translocon. Translocated proteins, synthesized as precursors with cleavable signal sequences, require cytoplasmic chaperones, such as SecB, to remain competent for posttranslational transport. In concert with SecB, SecA targets the precursors to SecY and energizes their translocation by its ATPase activity. The latter function involves a partial insertion of SecA itself into the SecYE translocon, a process that is strongly assisted by a couple of membrane proteins, SecG, SecD, SecF, YajC, and the proton gradient across the membrane. Integral membrane proteins, however, are specifically recognized by a direct interaction between their noncleaved signal anchor sequences and the bacterial signal recognition particle (SRP) consisting of Ffh and 4.5S RNA. Recognition occurs during synthesis at the ribosome and leads to a cotranslational targeting to SecYE that is mediated by FtsY and the hydrolysis of GTP. No other Sec protein is required for integration unless the membrane protein also contains long translocated domains that engage the SecA machinery. Discrimination between SecA/SecB- and SRP-dependent targeting involves the specificity of SRP for hydrophobic signal anchor sequences and the exclusion of SRP from nascent chains of translocated proteins by trigger factor, a ribosome-associated chaperone. The SecYE pore accepts only unfolded proteins. In contrast, a class of redox factor-containing proteins leaves the cell only as completely folded proteins. They are distinguished by a twin arginine motif of their signal sequences that by an unknown mechanism targets them to specific pores. A few membrane proteins insert spontaneously into the bacterial plasma membrane without the need for targeting factors and SecYE. Insertion depends only on hydrophobic interactions between their transmembrane segments and the lipid bilayer and on the transmembrane potential. Finally, outer membrane proteins of Gram-negative bacteria after having crossed the plasma membrane are released into the periplasm, where they undergo distinct folding events until they insert as trimers into the outer membrane. These folding processes require distinct molecular chaperones of the periplasm, such as Skp, SurA, and PpiD.
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Affiliation(s)
- M Müller
- Institute of Biochemistry and Molecular Biology, University of Freiburg, Germany
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Sarker S, Rudd KE, Oliver D. Revised translation start site for secM defines an atypical signal peptide that regulates Escherichia coli secA expression. J Bacteriol 2000; 182:5592-5. [PMID: 10986266 PMCID: PMC111006 DOI: 10.1128/jb.182.19.5592-5595.2000] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The secretion-responsive regulation of Escherichia coli secA occurs by coupling its translation to the translation and secretion of an upstream regulator, secM (formerly geneX). We revise the translational start site for secM, defining a new signal peptide sequence with an extended amino-terminal region. Mutational studies indicate that certain atypical amino acyl residues within this extended region are critical for proper secA regulation.
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Affiliation(s)
- S Sarker
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459, USA
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Woodbury RL, Topping TB, Diamond DL, Suciu D, Kumamoto CA, Hardy SJ, Randall LL. Complexes between protein export chaperone SecB and SecA. Evidence for separate sites on SecA providing binding energy and regulatory interactions. J Biol Chem 2000; 275:24191-8. [PMID: 10807917 DOI: 10.1074/jbc.m002885200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During localization to the periplasmic space or to the outer membrane of Escherichia coli some proteins are dependent on binding to the cytosolic chaperone SecB, which in turn is targeted to the membrane by specific interaction with SecA, a peripheral component of the translocase. Five variant forms of SecB, previously demonstrated to be defective in mediating export in vivo (Gannon, P. M., and Kumamoto, C. A. (1993) J. Biol. Chem. 268, 1590-1595; Kimsey, H. K., Dagarag, M. D., and Kumamoto, C. A. (1995) J. Biol. Chem. 270, 22831-22835) were investigated with respect to their ability to bind SecA both in solution and at the membrane translocase. We present evidence that at least two regions of SecA are involved in the formation of active complexes with SecB. The variant forms of SecB were all capable of interacting with SecA in solution to form complexes with stability similar to that of complexes between SecA and wild-type SecB. However, the variant forms were defective in interaction with a separate region of SecA, which was shown to trigger a change that was correlated to activation of the complex. The region of SecA involved in activation of the complexes was defined as the extreme carboxyl-terminal 21 aminoacyl residues.
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Affiliation(s)
- R L Woodbury
- School of Molecular Biosciences, Washington State University, Pullman, Washington 99164-4660, USA
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Volkert TL, Baleja JD, Kumamoto CA. A highly mobile C-terminal tail of the Escherichia coli protein export chaperone SecB. Biochem Biophys Res Commun 1999; 264:949-54. [PMID: 10544036 DOI: 10.1006/bbrc.1999.1590] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The Escherichia coli export chaperone SecB binds nascent precursors of certain periplasmic and outer membrane proteins and prevents them from folding or aggregating in the cytoplasm. In this study, we demonstrate that the C-terminal 13 residues of SecB were highly mobile using (1)H NMR spectroscopy. A protein lacking the C-terminal 13 amino acids of wild-type SecB was found to retain the ability to bind unfolded maltose-binding protein (MBP) in vitro but to interfere with the normal kinetics of pre-MBP export when overexpressed in vivo. The defect in export was reversed by overproduction of the peripheral membrane ATPase SecA. Therefore, deletion of the mobile region of SecB may alter the interactions of SecB with SecA.
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Affiliation(s)
- T L Volkert
- Department of Molecular Biology, Department of Biochemistry, Tufts University, 136 Harrison Avenue, Boston, Massachusetts, 02111, USA
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