SecA is an intrinsic subunit of the Escherichia coli preprotein translocase and exposes its carboxyl terminus to the periplasm

Abstract

SecA is the dissociable ATPase subunit of the Escherichia coli preprotein translocase, and cycles in a nucleotide-modulated manner between the cytosol and the membrane. Overproduction of the integral subunits of the translocase, the SecY, SecE and SecG polypeptides, results in an increased level of membrane-bound SecA. This fraction of SecA is firmly associated with the membrane as it is resistant to extraction with the chaotropic agent urea, and appears to be anchored by SecYEG rather than by lipids. Topology analysis of this membrane-associated form of SecA indicates that it exposes a carboxy-terminal domain to the periplasmic face of the membrane.

Glycolipozyme MPIase is essential for topology inversion of SecG during preprotein translocation

“…The activity was enhanced by SecYEG overproduction (Fig. 2 A and B), as reported (27)(28)(29). When the amount of SecYEG was examined by immunoblotting, ∼10-fold overproduction of each subunit was observed (Fig.…”

Multiple SecA Molecules Drive Protein Translocation across a Single Translocon with SecG Inversion

“…Therefore, the structures during translocation, such as that of SecYEG with inverted SecG or translocating preproteins, have not yet been clarified. Moreover, although SecYEG overproduction significantly enhances the translocation activity, the specific activity per SecYEG is quite low compared with in IMV prepared from the wild-type strain (45,50,51). Furthermore, SecG inversion could not be detected under the SecYEG-overproducing conditions (17,18), strongly suggesting the presence of unknown factor(s) involved in translocation.…”

Stoichiometry of SecYEG in the active translocase of Escherichia coli varies with precursor species

“…Once inserted, SecYEG could freely exchange the integrated SecA for soluble SecA. The SecA bound nonspecifically to lipid head groups via the C-domain (10,(42)(43)(44) might also be a source of SecA for exchange. It has been proposed previously that this membrane-bound pool of SecA facilitates binding to translocons as they become available (44).…”