Protein kinase C (PKC) 11 has been established to be the mainstay of several intracellular signaling systems, especially that related to Ca2 + mobilization. The myristoylated alanine-rich protein kinase C (MARCKS) substrate is a major substrate and is suggested to be involved in the cellular signaling pathway involving PKC activation (1).
Although the physiological function of MARCKS has not yet been clearly clarified, it has been suggested that the association of MARCKS with the plasma membrane or cytoskeleton (2) is of importance with respect to the function of MARCKS. MARCKS associates with the plasma membrane under regulation through PKC-catalyzed phosphorylation of MARCKS (3, 4). MARCKS has been suggested to be able to associate with the plasma membrane by binding to phospholipids without interaction with membranous proteins (5, 6, 10).
PKC (7), synaptotagmine (8), and clotting factor V (9) have been reported to bind specifically to phosphatidylserine (PS), and their binding domains have been reported. The interaction of coagulation factor V with the surface of platelets is considered to involve binding to PS. We previously reported that full-length recombinant MARCKS expressed in bacteria clearly bind to PS, as do MARCKS purified from rat brain (10). The binding of MARCKS to PS is removed in PKC-catalyzed phosphorylation. This is consistent with the reversible association of MARCKS with the plasma membrane. Therefore, it is very important to elucidate the physiological role of the PS binding of MARCKS. We have investigated the structure of MARCKS to bind to PS using a bacterial expression system. As a result, the Ca2 + independent PS binding domain of rat MARCKS was identified within a region 30 amino acid residues in length.