Ca2+-induced stimulation of the membrane binding of Escherichia coli SecA and its association with signal peptides of secretory proteins

Previously, it was found that Ca2+ stimulates the intrinsic Escherichia coli SecA ATPase activity [Kim et al., FEBS Lett. 493 (2001) 12–16]. Now, we suggest that Ca2+ is required for efficient interaction of SecA with membranes and the signal peptide of ribose-binding protein. When the amount of external Ca2+ was enhanced, the amounts of membrane-bound SecA and its lipid/ATPase activity increased. In the presence of entrapped Ca2+ in liposomes, the binding was also stimulated in a Ca2+ concentration-dependent manner. The effect of Ca2+ on the functional regulation of SecA was also evident in the presence of the signal peptides of secretory proteins, which the interaction of SecA with the signal peptide increased with increasing Ca2+ concentration in the presence of membranes. However, other divalent cations including Mg2+, Mn2+, and Zn2+ had inhibitory or no effect, suggesting a specific role of Ca2+ in SecA interaction with lipid bilayers and signal peptides.