PROSITE documentation PDOC01016

SecA family signature and profile

SecA is a cytoplasmic protein of 800 to 960 amino acid residues. The eubacterial secA protein [1] plays an important role in protein export. It interacts with the secY and secE components of the protein translocation system. It has a central role in coupling the hydrolysis of ATP to the transfer of proteins across the membrane.

SecA is a superfamily 2 (SF2) helicase (see <PDOC51192>) that adapted to translocate proteins. It contains the characteristic DEAD/DEXH ATPase core structure with the seven SF2 motifs [2,3].

Several structural analyses on secA have been reported (see <PDB:1M6N>) [4,5]. They show that secA contains two recA-like domains similar to SF1 and SF2 helicases. In helicases, the two recA-like domains move relative to one another during the ATPase cycle, generating domain movements that translocate the helicase along nucleic acids. In secA, it seems that a similar mechanism is used to generate domain movements that are coupled to polypeptide translocation. The N-terminal recA-like domain of secA contains an insert of about 150 residues that forms the preprotein crosslinking domain (PPXD) which has the ability to bind preproteins in solution and which is important for preprotein loading onto SecYEG-containing membranes [6].

Homologs of secA are also encoded in the chloroplast genome of some algae [7] as well as in the nuclear genome of plants [8]. It could be involved in the intraorganellar protein transport into thylakoids.

We have developed a signature pattern for secA proteins based on the best conserved region. This region is located in the C-terminal recA-like domain. We also developed a profile that covers the region corresponding to the two recA-like domains.