Differential roles of ionic, aliphatic, and aromatic residues in membrane-protein interactions: a surface plasmon resonance study on phospholipases A2.

The roles of cationic, aliphatic, and aromatic residues in the membrane association and dissociation of five phospholipases A(2) (PLA(2)), including Asp-49 PLA(2) from the venom of Agkistrodon piscivorus piscivorus, acidic PLA(2) from the venom of Naja naja atra, human group IIa and V PLA(2)s, and the C2 domain of cytosolic PLA(2), were determined by surface plasmon resonance analysis. Cationic interfacial binding residues of A. p. piscivorus PLA(2) (Lys-10) and human group IIa PLA(2) (Arg-7, Lys-10, and Lys-16), which mediate electrostatic interactions with anionic membranes, primarily accelerate the membrane association. In contrast, an aliphatic side chain of the C2 domain of cytosolic PLA(2) (Val-97), which penetrates into the hydrophobic core of the membrane and forms hydrophobic interactions, mainly slows the dissociation of membrane-bound protein. Aromatic residues of human group V PLA(2) (Trp-31) and N. n. atra PLA(2) (Trp-61, Phe-64, and Tyr-110) contribute to both membrane association and dissociation steps, and the relative contribution to these processes depends on the chemical nature and the orientation of the side chains as well as their location on the interfacial binding surface. On the basis of these results, a general model is proposed for the interfacial binding of peripheral proteins, in which electrostatic interactions by ionic and aromatic residues initially bring the protein to the membrane surface and the subsequent membrane penetration and hydrophobic interactions by aliphatic and aromatic residues stabilize the membrane-protein complexes, thereby elongating the membrane residence time of protein.