Preprotein translocase SecE subunit superfamily

This family is the protein translocase SEC61 complex gamma subunit of the archaeal and eukaryotic type. It does not hit bacterial SecE proteins. Sec61 is required for protein translocation in the endoplasmic reticulum.

The Sec61 complex (eukaryotes) or SecY complex (prokaryotes) forms a conserved heterotrimeric integral membrane protein complex and 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) [14661030, 11597451]. This complex is itself a part of a larger translocase heterotrimeric complex composed of alpha, beta and gamma subunits.

The channel is a passive conduit for polypeptides. It therefore has to 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 [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 [11597451]. In yeast (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 [14661030].