Protein transport protein SecG/Sec61-beta/Sbh (IPR016482)

Short name: SecG/Sec61-beta/Sbh

Overlapping homologous superfamilies


Family relationships


This family includes preprotein translocase subunit SecG, protein transport protein Sec61 subunit beta and Sbh1.

A conserved heterotrimeric integral membrane protein complex--the Sec61 complex (eukaryotes) or SecY complex (prokaryotes)--forms a protein-conducting channel that allows polypeptides to be transferred across (or integrated into) the endoplasmic reticulum (eukaryotes) or across the cytoplasmic membrane (prokaryotes) [PMID: 14661030, PMID: 11597451]. This complex is itself a part of a larger translocase complex.

The alpha subunits (IPR002208), called Sec61alpha in mammals, Sec61p in Saccharomyces cerevisiae (Baker's yeast), and SecY in prokaryotes, and the gamma subunits, called Sec61gamma in mammals, Sss1p in S. cerevisiae, and SecE in prokaryotes, show significant sequence conservation. Both subunits are required for cell viability in S. cerevisiae and Escherichia coli. The beta subunits, called Sec61beta in mammals, Sbh in S. cerevisiae, and SecG in archaea, are not essential for cell viability. They are similar in eukaryotes and archaea, but show no obvious homology to the corresponding SecG subunits in bacteria.

SecY forms the channel pore, and it is the cross-linking partner of polypeptide chains passing through the membrane [PMID: 14661030]. SecY and SecE constitute the high-affinity SecA-binding site on the membrane [PMID: 11597451]. The channel is a passive conduit for polypeptides. It must therefore associate with other components that provide a driving force. The partner proteins in bacteria and eukaryotes differ. In bacteria, the translocase complex comprises 7 proteins [PMID: 14661030], including a chaperone protein (SecB), an ATPase (SecA), an integral membrane complex (SecY, SecE and SecG), and two additional membrane proteins that promote the release of the mature peptide into the periplasm (SecD and SecF). The SecA ATPase interacts dynamically with the SecYEG integral membrane components to drive the transmembrane movement of newly synthesized preproteins [PMID: 11597451]. In S. cerevisiae (and probably in all eukaryotes), the full translocase comprises another membrane protein subcomplex (the tetrameric Sec62/63p complex), and the lumenal protein BiP, a member of the Hsp70 family of ATPases. BiP promotes translocation by acting as a molecular ratchet, preventing the polypeptide chain from sliding back into the cytosol [PMID: 14661030].

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.