Deregulation of the SecYEG Translocation Channel upon Removal of the Plug Domain

Antoine P Maillard,Franck Duong,Dominique Belin,Shifana Lalani,Filo Silva

doi:10.1074/jbc.m610060200

Antoine P Maillard, Franck Duong + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m610060200

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Abstract

Previous studies have shown that the SecY plug is displaced from the center of the SecYEG channel during polypeptide translocation. The structural and functional consequences of the deletion of the plug are now examined. Both in vivo and in vitro observations indicate that the plug domain is not essential to the function of the translocon. In fact, deletion of the plug confers to the cell and to the membranes a Prl-like phenotype: reduced proton-motive force dependence of translocation, increased membrane insertion of SecA, diminished requirement for functional leader peptide, and weakened SecYEG subunit association. Although the plug domain does not seem essential, locking the plug in the center of the channel inactivates the translocon. Thus, the SecY plug is important to regulate the activity of the channel and to confer specificity to the translocation reaction. We propose that the plug contributes to the gating mechanism of the channel by maintaining the structure of the SecYEG complex in a compact closed state.

Highlights

The Sec translocon is a universally conserved membrane protein complex that cooperates with cytosolic partners to transport proteins into or across membranes
The crystal structure of the Methanococcus jannaschii SecY complex [6] has unraveled the architecture of the core translocon. It consists of four key structural elements: the “channel,” located in the body of the SecY subunit; the “pore ring” made of 6 residues forming a constriction point in the middle of the channel; the “plug” domain formed by a small helix seating on top of the constriction on its periplamic side; and the “lateral gate” made by the juxtaposition of two SecY transmembrane (TM2 and TM7) segments that create an opening toward the lipid bilayer
The crystal structure shows that most of the prl mutations are located in the pore ring or in the plug domain, and these mutations may destabilize the closed state of the channel [6]

Summary

Introduction

The Sec translocon is a universally conserved membrane protein complex that cooperates with cytosolic partners to transport proteins into or across membranes. Deletion of the plug confers to the cell and to the membranes a Prl-like phenotype: reduced proton-motive force dependence of translocation, increased membrane insertion of SecA, diminished requirement for functional leader peptide, and weakened SecYEG subunit association.

Results

Conclusion