DOMAIN ORGANIZATION OF BACILLUS-THURINGIENSIS CRYIIIA DELTA-ENDOTOXINSTUDIED BY DENATURATION IN GUANIDINE-HYDROCHLORIDE SOLUTIONS AND LIMITED PROTEOLYSIS

Denaturation of Bacillus thuringiensis CryIIIA delta-endotoxin-an inse cticidal protein, active against Coleoptera larvae-in concentrated gua nidine hydrochloride solutions was pursued by fluorescence and circula r dichroism spectroscopy and limited proteolysis. It was found that th e protein consists of two fragments that differ by their stability to denaturation by guanidine hydrochloride at pH 3. The less stable fragm ent corresponds to the N-terminal alpha-helical domain limited by Leu- 279; the more stable one starts with Ile-280, contains about 330 amino acid residues, and corresponds to the molecule C-terminal moiety that consist of its two beta-structural domains forming a superdomain.