Surfing the channel

Jermy, Andrew

doi:10.1038/nrmicro2037

Research Highlight
Published: 03 November 2008

Bacterial secretion

Surfing the channel

Andrew Jermy

Nature Reviews Microbiology volume 6, page 877 (2008)Cite this article

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Most bacterial proteins that are inserted into, or translocated across, the plasma membrane are targeted to the evolutionarily conserved SecY translocon complex. Three papers published in Nature now provide insight into how the cytoplasmic ATPase SecA moves polypeptides through the SecY channel.

Zimmer, Rapoport and colleagues now report crystal structures of SecA that are associated with SecY complexes. In the structures, a single copy of SecA was bound to each SecY complex, and this interaction led to substantial conformational changes in both partners. In the SecY-bound state, the SecA polypeptide cross-linking domain (PPXD) rotated from its original position to contact nucleotide-binding domain 2 (NBD2). This interface aligned perfectly with the channel opening in SecY, leading the authors to propose that PPXD and NBD2 form a clamp that captures and aligns substrates for insertion into the pore. Interestingly, upon binding to SecA, conformational changes in SecY led to the widening of the lateral gate but not complete displacement of the plug domain. A similar rearrangement was observed by Tsukazaki, Nureki and colleagues, who found that anti-SecY Fab fragments, which bind to the same site as SecA, promoted expansion of the lateral gate to form a hydrophobic crevasse. These observations point to formation of a 'pre-open' state, in which the translocation channel is primed but not yet completely open.

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ORIGINAL RESEARCH PAPERS

Zimmer, J. et al. Structure of a complex of the ATPase SecA and the protein-translocation channel. Nature 455, 936–943 (2008)
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Erlandson, K. J. et al. A role for the two-helix finger of the SecA ATPase in protein translocation. Nature 455, 984–987 (2008)
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Tsukazaki, T. et al. Conformational transition of Sec machinery inferred from bacterial SecYE structures. Nature 455, 988–991 (2008)
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