The essentiality of B chain in stabilizing the structure of the A chain in β1-bungarotoxin fromBungarus multicinctus venom

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Abstract
The dynamic of Trp residue inΒ1-bungarotoxin (gb1-Bgt), the A chain ofΒ1-Bgt and phospholipase A2 (PLA2) was assessed by fluorescence measurement. Acrylamide quenching studies showed that the exposure degree of the Trp in PLA2 is higher than the Trp inΒ1-Bgt. The Trp ofΒ1-Bgt had a higher accessibility for iodide, reflecting that the basic nature of the B chain might exert an attractive electrostatic force for iodide and increase the susceptibility of Trp in the A chain to iodide. Removal of the B chain ofΒ1-Bgt did not significantly affect the exposure degree of Trp in the A chain. Alternatively, the polarity of the environment around the Trp and the hydrophobic character of ANS and substrate binding sites in the separated A chain changed. Measurement of Trp fluorescence with increasing temperature showed that the stability of structure ofΒ1-Bgt was higher than those of the separated A chain and PLA2. These results suggest that the B chain might interact with the A chain and stabilize the conformation of the A chain inΒ1-Bgt.