Membrane-damaging activity with A chain and B chain of beta-bungarotoxin

Beta-bungarotoxin (beta-Bgt) consists of A chain (a phospholipase A2 subunit) and B chain, cross-linked by an intersubunit disulfide bridge. In contrast to a marginal activity noted with beta-Bgt, recombinant A1 chain and B1 chain markedly induced release of calcein from phospholipid vesicles. Reduction of intersubunit disulfide bond by dithiothreitol or glutathione enhanced membrane-damaging activity of beta-Bgt. Moreover, phospholipid-binding capability of recombinant A1 and B1 chains was higher than that of beta-Bgt. In contrast to beta-Bgt, A1 and B1 chains preferably bound lipids with a preference for anionic over zwitterionic phospholipids. Removal of positively charged residues lying on the interface between A chain and B chain resulted in abolishment of membrane-permeabilizing activity of B chain. Taken together, our data indicate that both A and B chains possess the capability to induce vesicle leakage, and reduction of interchain disulfide bond markedly releases this ability from intact beta-Bgt molecule.