Activation of the Bacillus thuringiensis subesp. medellin CryllBb protein by digestion with trypsin and Culex quinquefasciatus (Diptero: Culicidae) larval gut extracts

Abstract

The ability of the larval midgut protease extracts from Culex quinquefaseiatus and trypsin to process Bacillus thuringiensis subsp. medellin Cry 11 Bb toxin was investigated. The activity of midgut proteases increases with an increment in pH being the highest activity obtained at pH 10.6. A time-course study showed partial fragmentation of the protein ultimately ending in the produc­tion of protease-resistant core fragments of relative molecular masses of 30 and 33 kDa. Proteases with trypsin specificity were detected in C. quinquefasciatus larval midgut extracts. This activity was detected by N-ter­minal amino acid sequence analysis of the Badilas thuringiensis subsp. medellin CryllBb toxin proteolytic fragments. In vivo, the mosquito larvae processed the inclusions generating three fragments. The fragments fully retain their toxicity to C. quinque­fasciatus first instar larvae. These data indicate the possible role of midgut proteases in B. thuringiensis subsp. medellin CryllB b toxin activation.