Poramed ChayaratanasinSeangdeun MoonsomSomsri SakdeeUrai ChaisriGerd KatzenmeierChanan AngsuthanasombatMahidol University2018-08-242018-08-242007-01-01Journal of Biochemistry and Molecular Biology. Vol.40, No.1 (2007), 58-6402191024122586872-s2.0-33846609664https://repository.li.mahidol.ac.th/handle/20.500.14594/24270Similar to the other known structures of Bacillus thuringiensis Cry δ-endotoxins, the crystal structure of the 65-kDa activated Cry4Ba toxin comprises three domains which are, from the N- to C-terminus, a bundle of α-helices, a three-β-sheet domain, and a β-sandwich. To investigate the properties of the C-terminal domain III in isolation from the rest of the toxin, the cloned Cry4Ba-domain III was over-expressed as a 21-kDa soluble protein in Escherichia coli, which cross-reacted with anti-Cry4Ba domain III monoclonal antibody. A highly-purified domain III was obtained in a monomeric form by ion-exchange and size-exclusion FPLC. Circular dichroism spectroscopy indicated that the isolated domain III fragment distinctly exists as a β-sheet structure, corresponding to the domain III structure embodied in the Cry4Ba crystal structure. In vitro binding analysis via immuno-histochemical assay revealed that the Cry4Ba-domain III protein was able to bind to the apical microvilli of the susceptible Stegomyia aegypti larval midguts, albeit at lower-binding activity when compared with the full-length active toxin. These results demonstrate for the first time that the C-terminal domain III of the Cry4Ba mosquito-larvicidal protein, which can be isolated as a native folded monomer, conceivably participates in toxin-receptor recognition.Mahidol UniversityBiochemistry, Genetics and Molecular BiologyArticleSCOPUS