cDNA sequence analysis and expression of the a chain of beta-bungarotoxin from Bungarus multicinctus (Taiwan banded krait).

The cDNA encoding the A chain of beta-bungarotoxin (beta-Bgt) was constructed from the cellular RNA isolated from the venom glands of Bungarus multicinctus (Taiwan banded krait). The deduced amino acid sequence encoding the A chain revealed that the determined one was different from the known A chains (A1, A2, A3 and A4). Nevertheless, the amino acid sequence and cDNA sequence of the new A chain (A5) was highly homologous with those of other A chains. The A5 chain was subcloned into the expression vector pT7-7 and transformed into BL21(DE3) E. coli strain. The expressed protein was isolated from the inclusion bodies of E. coli, and the refolded A chain was purified by reversed phase high performance liquid chromatography. The purified recombinant A chain exhibited an about 16% phospholipase activity of beta-Bgt. These results strongly suggest that the A chain is an active subunit responsible for the phospholipase activity of beta-Bgt.