Molecular cloning and functional characterization of SecE of a marine bacterium, Vibrio alginolyticus.

SecE is an essential membrane component of the Escherichia coli protein translocation machinery, which utilizes ATP and the proton motive force as energy sources. The secE homologue of marine Vibrio alginolyticus, in which protein translocation requires ATP and the sodium motive force, was cloned, sequenced, and characterized. Unlike most SecE homologues found in various organisms, SecE of V. alginolyticus (Va-SecE) possesses three transmembrane sequences like E. coli SecE (Ec-SecE) and complements the DeltasecE mutation of E. coli. Alignment of the Ec-SecE and Va-SecE sequences revealed that the non-essential N-terminal half was less homologous than the essential C-terminal half between the two SecEs. The E. coli strain was able to grow and translocate the secretory protein in the complete absence of Ec-SecE when Va-SecE was expressed. The stabilization of SecY overproduction by Va-SecE was as effective as that by Ec-SecE, indicating that Va-SecE interacts with E. coli SecY despite the difference in energy requirement.