An oligomeric complex of BinA/BinB is not formed in-situ in mosquito-larvicidal Lysinibacillus sphaericus ISPC-8.

Binary toxin of Lysinibacillus sphaericus is composed of two polypeptides; receptor binding BinB and toxic BinA. Both the polypeptides are required for maximal toxicity. It has been suggested that binary toxin exerts toxicity as a heterotetramer constituted by two copies of each of the component polypeptides. It has also been observed that oligomers consisting of two copies of BinA and BinB are pre-formed in L. sphaericus spore-crystals. However, recombinant proteins from Escherichia coli expression system elute individually as monomers. We purified the likely oligomeric complex from the spore-crystals of highly toxic L. sphaericus ISPC-8 strain and probed it with proteomic tools. The analysis showed that the high molecular mass complex in the toxic spore-crystals is composed of only surface layer protein (SlpC). The purified SlpC from the local isolate exists as a dimer and also showed poor mosquito-larvicidal activity.