| Primary Identifier | IPR024912 | Type | Family |
| Short Name | SecD_arc |
| description | Secretion across the inner membrane in some Gram-negative bacteria occurs via the preprotein translocasepathway. Proteins are produced in the cytoplasm as precursors, and require a chaperone subunit to direct them tothe translocase component []. From there, the mature proteins are either targeted to the outermembrane, or remain as periplasmic proteins. The translocase protein subunits are encoded on the bacterialchromosome. The translocase itself comprises 7 proteins, including a chaperone protein (SecB), an ATPase (SecA), an integralmembrane complex (SecCY, SecE and SecG), and two additional membrane proteins that promote the release ofthe mature peptide into the periplasm (SecD and SecF) []. The chaperone protein SecB []is a highly acidic homotetrameric protein that exists as a "dimer of dimers"in the bacterial cytoplasm.SecB maintains preproteins in an unfolded state after translation, and targets these to the peripheral membraneprotein ATPase SecA for secretion []. Together with SecY and SecG, SecE forms a multimericchannel through which preproteins are translocated, using both proton motive forces and ATP-driven secretion. Thelatter is mediated by SecA. The structure of theEscherichia coli SecYEG assembly revealed a sandwich of two membranes interacting through the extensive cytoplasmicdomains []. Each membrane is composed of dimers of SecYEG. The monomeric complex contains 15transmembrane helices. The SecD and SecF equivalents of theGram-positive bacterium Bacillus subtilis are jointly present in one polypeptide,denoted SecDF, that is required to maintain a high capacity for protein secretion.Unlike the SecD subunit of the pre-protein translocase of E. coli, SecDFof B. subtilis was not required for the release of a mature secretory protein fromthe membrane, indicating that SecDF is involved in earlier translocation steps [].Comparison with SecD andSecF proteins from other organisms revealed the presence of 10 conservedregions in SecDF, some of which appear to be important for SecDF function.Interestingly, the SecDF protein of B. subtilis has 12 putative transmembranedomains. Thus, SecDF does not only show sequence similarity but also structuralsimilarity to secondary solute transporters [].This family consists of various archaeal SecD proteins. They show a high degree of structural and functional similarity to their bacterial homologues, despite the different composition of their translocation machineries []. |
