Involvement of an endogenous metalloprotease in the activation of protoxin in Bacillus thuringiensis subsp. kurstaki

Abstract

Insecticidal crystal proteins harvested from sporulated cultures of Bacillus thuringiensis subsp. kurstaki contain the protoxin (Mr 132 kDa) and minor amounts of toxin (66 kDa). The proteolytic processing of 132 kDa protoxin to an active 66 kDa toxin is brought about by exogenous proteases or larval gut enzymes. Under denaturing/reducing conditions this conversion is also mediated by endogenous protease(s) of the producer organism. This endogenous protease is identified as a metalloprotease as the activation process is inhibited by ethylenediamine tetraacetic acid at 2 mM concentration.