M. Sumandea et al., Roles of aromatic residues in high interfacial activity of Naja naja atra phospholipase A(2), BIOCHEM, 38(49), 1999, pp. 16290-16297
Acidic phospholipase A(2) (PLA(2)) from the venom of Chinese cobra (Naja na
ja atra) has high activity on zwitterionic membranes and contains six aroma
tic residues, including Tyr-3, Trp-18, Trp-19, Trp-61, Phe-64, and Tyr-110,
on its putative interfacial binding surface. To assess the roles of these
aromatic residues in the interfacial catalysis of N, n, arm PLA(2), we muta
ted them to Ala and measured the effects on its interfacial catalysis. Enzy
matic activities of the mutants toward various vesicle substrates and human
neutrophils indicate that all but Trp-18 make significant contributions to
interfacial catalysis. Among these aromatic residues, Trp-19, Trp-61, and
Phe-64 play the most important roles. Binding affinities of the mutants for
phospholipid-coated beads and their monolayer penetration indicate that Tr
p-19, Trp-61, and Phe-64 are critically involved in interfacial binding of
N. n. atra PLA(2) and penetrate into the membrane during the interfacial ca
talysis of N. n. atra PLA(2). Further thermodynamic analysis suggests that
the side chain of Phe-64 is fully inserted into the hydrophobic core of mem
brane whereas these of Trp-19 and Trp-61 are located in the membrane-water
interface. Together, these results show that all three types of aromatic re
sidues can play important roles in interfacial binding of PLA(2) depending
on their location and side-chain orientation. They also indicate that these
aromatic side chains interact with membranes in distinct modes because of
their different intrinsic preference for different parts of membranes.