Separable ATPase and membrane insertion domains of the SecA subunit of preprotein translocase.

The SecA subunit of preprotein translocase drives ATP-dependent translocation of preproteins across the bacterial inner membrane concomitant with cycles of membrane insertion and de-insertion (Economou, A., and Wickner, W. (1994) Cell 78, 835-843). We have identified the membrane-inserting region of SecA as a 30-kDa domain in the C-terminal third of the protein beginning at aminoacyl residue 610. Limited proteolysis in the absence of translocation ligands indicates that the SecA monomer is composed of two primary structural domains, the 30-kDa membrane-inserting domain and an N-terminal 65-kDa ATPase domain. This limited protease treatment of SecA results in constitutive ATPase activity, indicating that intramolecular constraints between the two domains may play a role in the regulation of ATP hydrolysis by SecA.