THE CYTOPLASMIC DOMAIN OF MYELIN GLYCOPROTEIN P-0 INTERACTS WITH NEGATIVELY CHARGED PHOSPHOLIPID-BILAYERS

The intracellular COOH-terminal domain of the glycoprotein, P-0, has b een proposed to be involved in the formation of the major dense line o f peripheral myelin. We have addressed this hypothesis by generating a nd subsequently isolating a peptide fragment that contains 65 of the 6 9 residues of the cytoplasmic region of rat P-0. This peptide, termed P-0(intra), bound to artificial phospholipid vesicles and caused their rapid aggregation. The peptide-induced aggregation of membrane bilaye rs appeared to result from ionic interactions, since P-0(intra)-vesicl e association was decreased by 1) reducing the phosphatidylserine cont ent of the membranes, 2) increasing the NaCl concentration of the surr ounding buffer, or 3) elevating the divalent cation concentration with in the buffers. Cationic disc gel electrophoresis of P-0(intra), revea led at least four charge isoforms of the peptide. Treatment of sciatic nerve slices with phorbol ester prior to isolation of P-0(intra), inc reased the amount of the more negatively charged species, suggesting t hat at least some of the charge heterogeneity of the peptide can be at tributed to differing phosphorylation states. The ability of P-0(intra ), to bind to phospholipid bilayers implies that the cytoplasmic domai n of P-0 may be responsible for the formation and maintenance of the m yelin major dense line.