Shanmugavelu M, Rajamohan F, Kathirvel M, Elangovan G, Dean D H, Jayaraman K
Centre for Biotechnology, Anna University, Madras, India.
Appl Environ Microbiol. 1998 Feb;64(2):756-9. doi: 10.1128/AEM.64.2.756-759.1998.
Alanine residues were substituted by site-directed mutagenesis at selected sites of the N- and C-terminal regions of the binary toxin (51- and 42-kDa peptides) of B. sphaericus 1593M, and the mutant toxins were cloned and expressed in Escherichia coli. Bioassays with mosquito larvae, using binary toxins derived from individual mutants, showed that the substitution of alanine at some sites in both the 51-kDa and the 42-kDa peptides resulted in a total loss of activity. Surprisingly, after mixing two nontoxic derivatives of the same peptide, i.e., one mutated at the N-terminal end and the other mutated at the C-terminal end of either the 51-kDa or the 42-kDa peptide, the toxicity was restored. This result indicates that the altered binary toxins can functionally complement each other by forming oligomers.
通过定点诱变，在球形芽孢杆菌1593M二元毒素（51 kDa和42 kDa肽段）的N端和C端区域的选定位点替换丙氨酸残基，然后将突变毒素克隆并在大肠杆菌中表达。使用来自单个突变体的二元毒素对蚊幼虫进行生物测定，结果表明，在51 kDa和42 kDa肽段的某些位点替换丙氨酸会导致活性完全丧失。令人惊讶的是，将同一肽段的两种无毒衍生物混合，即51 kDa或42 kDa肽段的一个在N端突变，另一个在C端突变后，毒性得以恢复。这一结果表明，改变后的二元毒素可通过形成寡聚体在功能上相互补充。
