THE ATPASE ACTIVITY OF SECA IS REGULATED BY ACIDIC PHOSPHOLIPIDS, SECY, AND THE LEADER AND MATURE DOMAINS OF PRECURSOR PROTEINS

The ATPase activity of SecA is stimulated by E. coli plasma membrane vesicles bearing SecY protein and a precursor protein such as proOmpA. This activity is termed "translocation ATPase": Liposomes alone can also stimulate SecA ATPase, but membrane proteins block this stimulation in native inner membranes. We define the stimulation of SecA ATPase by lipid as "SecA/lipid ATPase". SecA/lipid ATPase, translocation ATPase, and translocation into inner membrane vesicles require acidic phospholipids, suggesting an underlying unity of mechanism. ProOmpA and ATP stabilize liposome-bound SecA. Full SecA/lipid ATPase activity and stability are also seen when a mixture of a leader peptide and either OmpA or maltose binding protein (MBP) are added instead of proOmpA, while neither the leader peptide alone nor OmpA or MBP suffice. Cytosolic proteins in conjunction with a leader peptide are less active in this reaction, indicating that liposome-bound SecA protein recognizes both leader and mature domains. © 1990.