title: Two-way communication between SecY and SecA suggests a Brownian ratchet mechanism for protein translocation.
abstract: The essential process of protein secretion is achieved by the ubiquitous Sec machinery. In prokaryotes, the drive for translocation comes from ATP hydrolysis by the cytosolic motor-protein SecA, in concert with the proton motive force (PMF). However, the mechanism through which ATP hydrolysis by SecA is coupled to directional movement through SecYEG is unclear. Here, we combine all-atom molecular dynamics (MD) simulations with single molecule FRET and biochemical assays. We show that ATP binding by SecA causes opening of the SecY-channel at long range, while substrates at the SecY-channel entrance feed back to regulate nucleotide exchange by SecA. This two-way communication suggests a new, unifying 'Brownian ratchet' mechanism, whereby ATP binding and hydrolysis bias the direction of polypeptide diffusion. The model represents a solution to the problem of transporting inherently variable substrates such as polypeptides, and may underlie mechanisms of other motors that translocate proteins and nucleic acids.
authors.affiliation: School of Biochemistry, University of Bristol, Bristol, United Kingdom.
authors.forename: William John
authors.identifier: 0000-0002-9513-4786
authors.initials: WJ
authors.lastname: Allen
authors.affiliation: School of Biochemistry, University of Bristol, Bristol, United Kingdom.
authors.forename: Robin Adam
authors.initials: RA
authors.lastname: Corey
authors.affiliation: Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.|School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom.
authors.forename: Peter
authors.initials: P
authors.lastname: Oatley
authors.affiliation: School of Biochemistry, University of Bristol, Bristol, United Kingdom.
authors.forename: Richard Barry
authors.initials: RB
authors.lastname: Sessions
authors.affiliation: Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.|School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom.
authors.forename: Steve A
authors.initials: SA
authors.lastname: Baldwin
authors.affiliation: Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.|School of Molecular and Cellular Biology, University of Leeds, Leeds, United Kingdom.
authors.forename: Sheena E
authors.identifier: 0000-0002-3079-8039
authors.initials: SE
authors.lastname: Radford
authors.affiliation: Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom.|School of Molecular and Cellular Biology, University of Leeds, Leeds, United Kingdom.
authors.forename: Roman
authors.initials: R
authors.lastname: Tuma
authors.affiliation: School of Biochemistry, University of Bristol, Bristol, United Kingdom.
authors.forename: Ian
authors.identifier: 0000-0002-3931-0503
authors.initials: I
authors.lastname: Collinson
mesh_terms: D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D007700:Kinetics; D063747:Methanocaldococcus / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D054730:Protein Interaction Domains and Motifs; D021381:Protein Transport; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000069816:SEC Translocation Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000081416:SecA Proteins; D013379:Substrate Specificity; D013816:Thermodynamics; D020124:Thermotoga maritima / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D011994:Recombinant Proteins; D000069816:SEC Translocation Channels; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins
keywords: E. coli; SecA; SecYEG; biochemistry; biophysics; molecular dynamics; protein secretion; protein translocation; single molecule FRET; structural biology