title: Unusual amino acid determinants of host range in the Mtx2 family of mosquitocidal toxins.
abstract: Five different mosquitocidal toxin (mtx2) gene homologs have been cloned from eight Bacillus sphaericus strains. Pairwise comparisons of the predicted amino acid sequences show between four and eight substitutions compared with the prototype Mtx2 from B. sphaericus strain SSII-1. Mtx2 from strain SSII-1 was approximately 7-fold more toxic to Culex mosquito larvae than the Mtx2 homolog from B. sphaericus strain 31-2. Conversely, Mtx2 from strain 31-2 was approximately 100-fold more toxic to Aedes mosquito larvae than Mtx2 from strain SSII-1. Lys224 in Mtx2 was found to be the most important amino acid for toxicity to Culex larvae, and substitution of Lys224 with threonine abolished the toxicity of Mtx2 from strain SSII-1 to these larvae. In complete contrast, Thr224 was found to be crucial for the toxicity of Mtx2 from strain 31-2 to Aedes larvae, and substitution of Thr224 with lysine caused a approximately 100-fold drop in toxicity to these larvae. Thus, amino acid 224 in the Mtx2 family of mosquitocidal toxins is an unusual and important determinant of mosquito larvicidal activity and host range.
authors.affiliation: Institute of Molecular and Cell Biology, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Republic of Singapore.
authors.forename: S W
authors.initials: SW
authors.lastname: Chan
authors.forename: T
authors.initials: T
authors.lastname: Thanabalu
authors.forename: B Y
authors.initials: BY
authors.lastname: Wee
authors.forename: A G
authors.initials: AG
authors.lastname: Porter
mesh_terms: D000330:Aedes; D000595:Amino Acid Sequence; D000818:Animals; D001407:Bacillus / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics* / Q000633:toxicity; D001427:Bacterial Toxins; D001483:Base Sequence; D003001:Cloning, Molecular; D003465:Culex; D017931:DNA Primers; D005798:Genes, Bacterial; D007306:Insecticides; D007814:Larva; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000633:toxicity; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D017931:DNA Primers; D007306:Insecticides; C099210:Mtx2 protein, Bacillus sphaericus; D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins