INTERACTION OF MYRISTOYLATED ALANINE-RICH PROTEIN-KINASE-C SUBSTRATE (MARCKS) WITH MEMBRANE PHOSPHOLIPIDS

A major in vivo substrate of Ca2+-phospholipid-dependent protein kinase (MARCKS) shows phosphorylation-dependent translocation between the cytoplasmic and the membrane fractions. The mechanism of the translocation was studied with purified MARCKS and various membranes. MARCKS was found to bind to pure phospholipid membranes as well as to the synaptic vesicle membranes. Although the interaction of MARCKS with the latter was phosphorylation-dependent, phosphorylation by protein kinase C showed no significant effect on the binding to the phosphatidylcholine liposomes. However, when phosphatidylserine was included in the membranes, the association became phosphorylation-dependent. A synthetic phosphorylation domain peptide showed a similar phosphorylation-dependent interaction with the negatively charged liposomes. Phosphatidylserine but not phosphatidylcholine inhibited phosphorylation of MARCKS by protein kinase C. MARCKS seems to bind to the biomembranes through two binding sites: the N-terminal myristoyl moiety and the basic phosphorylation domain of amphiphilic nature. Phosphorylation of this domain lowers its affinity to phosphatidylserine and makes the whole molecule strongly negatively charged, which causes its dissociation from the membranes.