SecY

SecY is the core membrane protein of the bacterial Sec translocon, a protein-conducting channel that moves polypeptides across and into membranes. In bacteria, SecY forms the SecYEG complex with SecE and SecG in the inner membrane, where it serves as the central conduit for secretory and membrane proteins. Preproteins bearing N-terminal signal peptides are targeted to the translocon by various pathways, including the SRP pathway and SecA-dependent routes, and SecY provides the channel through which these polypeptides pass. Translocation energy is provided by the ATPase SecA and, for some steps, the proton motive force.

Structurally, SecY is an integral membrane protein with multiple transmembrane helices that assemble to form a central pore. A plug domain blocks the channel in the resting state, and a lateral gate allows hydrophobic segments to exit into the lipid bilayer as membrane proteins are formed. The SecY channel interacts with cytosolic components such as SecA and can associate with ribosomes during co-translational translocation.

SecY is highly conserved and is regarded as the prokaryotic counterpart to the eukaryotic Sec61 translocon. Eukaryotic Sec61, as well as SecY-like proteins in chloroplasts and mitochondria, share structural and functional similarities, reflecting a common evolutionary origin. The SecY protein is essential for viability in many bacteria; defects in SecY or its associated complex can disrupt protein export and membrane protein biogenesis.

See also: SecA, SecE, SecG, Sec61, protein translocation, SRP pathway.