Two-way communication between SecY and SecA suggests a Brownian ratchet mechanism for protein translocation

  1. William John Allen
  2. Robin Adam Corey
  3. Peter Oatley
  4. Richard Barry Sessions
  5. Sheena E Radford
  6. Roman Tuma
  7. Ian Collinson  Is a corresponding author
  1. University of Bristol, United Kingdom
  2. University of Leeds, United Kingdom

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.

Article and author information

Author details

  1. William John Allen

    School of Biochemistry, University of Bristol, Bristol, United Kingdom
    Competing interests
    The authors declare that no competing interests exist.
  2. Robin Adam Corey

    School of Biochemistry, University of Bristol, Bristol, United Kingdom
    Competing interests
    The authors declare that no competing interests exist.
  3. Peter Oatley

    Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
    Competing interests
    The authors declare that no competing interests exist.
  4. Richard Barry Sessions

    School of Biochemistry, University of Bristol, Bristol, United Kingdom
    Competing interests
    The authors declare that no competing interests exist.
  5. Sheena E Radford

    AStbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
    Competing interests
    The authors declare that no competing interests exist.
  6. Roman Tuma

    Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
    Competing interests
    The authors declare that no competing interests exist.
  7. Ian Collinson

    School of Biochemistry, University of Bristol, Bristol, United Kingdom
    For correspondence
    ian.collinson@bristol.ac.uk
    Competing interests
    The authors declare that no competing interests exist.

Copyright

© 2016, Allen et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

Metrics

  • 5,237
    views
  • 1,092
    downloads
  • 94
    citations

Views, downloads and citations are aggregated across all versions of this paper published by eLife.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. William John Allen
  2. Robin Adam Corey
  3. Peter Oatley
  4. Richard Barry Sessions
  5. Sheena E Radford
  6. Roman Tuma
  7. Ian Collinson
(2016)
Two-way communication between SecY and SecA suggests a Brownian ratchet mechanism for protein translocation
eLife 5:e15598.
https://doi.org/10.7554/eLife.15598

Share this article

https://doi.org/10.7554/eLife.15598

Further reading

    1. Biochemistry and Chemical Biology
    Meina He, Yongxin Tao ... Wenli Chen
    Research Article

    Copper is an essential enzyme cofactor in bacteria, but excess copper is highly toxic. Bacteria can cope with copper stress by increasing copper resistance and initiating chemorepellent response. However, it remains unclear how bacteria coordinate chemotaxis and resistance to copper. By screening proteins that interacted with the chemotaxis kinase CheA, we identified a copper-binding repressor CsoR that interacted with CheA in Pseudomonas putida. CsoR interacted with the HPT (P1), Dimer (P3), and HATPase_c (P4) domains of CheA and inhibited CheA autophosphorylation, resulting in decreased chemotaxis. The copper-binding of CsoR weakened its interaction with CheA, which relieved the inhibition of chemotaxis by CsoR. In addition, CsoR bound to the promoter of copper-resistance genes to inhibit gene expression, and copper-binding released CsoR from the promoter, leading to increased gene expression and copper resistance. P. putida cells exhibited a chemorepellent response to copper in a CheA-dependent manner, and CsoR inhibited the chemorepellent response to copper. Besides, the CheA-CsoR interaction also existed in proteins from several other bacterial species. Our results revealed a mechanism by which bacteria coordinately regulated chemotaxis and resistance to copper by CsoR.

    1. Biochemistry and Chemical Biology
    2. Immunology and Inflammation
    Pavla Nedbalová, Nikola Kaislerova ... Tomáš Doležal
    Research Article

    During parasitoid wasp infection, activated immune cells of Drosophila melanogaster larvae release adenosine to conserve nutrients for immune response. S-adenosylmethionine (SAM) is a methyl group donor for most methylations in the cell and is synthesized from methionine and ATP. After methylation, SAM is converted to S-adenosylhomocysteine, which is further metabolized to adenosine and homocysteine. Here, we show that the SAM transmethylation pathway is up-regulated during immune cell activation and that the adenosine produced by this pathway in immune cells acts as a systemic signal to delay Drosophila larval development and ensure sufficient nutrient supply to the immune system. We further show that the up-regulation of the SAM transmethylation pathway and the efficiency of the immune response also depend on the recycling of adenosine back to ATP by adenosine kinase and adenylate kinase. We therefore hypothesize that adenosine may act as a sensitive sensor of the balance between cell activity, represented by the sum of methylation events in the cell, and nutrient supply. If the supply of nutrients is insufficient for a given activity, adenosine may not be effectively recycled back into ATP and may be pushed out of the cell to serve as a signal to demand more nutrients.