Adaptive evolution of cry genes in Bacillus thuringiensis: implications for their specificity determination.
The cry gene family, produced during the late exponential phase of growth in Bacillus thuringiensis, is a large, still-growing family of homologous genes, in which each gene encodes a protein with strong specific activity against only one or a few insect species. Extensive studies are mostly focusing on the structural and functional relationships of Cry proteins, and have revealed several residues or domains that are important for the target recognition and receptor attachment. In this study, we have employed a maximum likelihood method to detect evidence of adaptive evolution in Cry proteins, and have identified 24 positively selected residues, which are all located in Domain II or III. Combined with known data from mutagenesis studies, the majority of these residues, at the molecular level, contribute much to the insect specificity determination. We postulate that the potential pressures driving the diversification of Cry proteins may be in an attempt to adapt for the "arm race" between delta-endotoxins and the targeted insects, or to enlarge their target spectra, hence result in the functional divergence. The sites identified to be under positive selection would provide targets for further structural and functional analyses on Cry proteins.
Wu
Jin-Yu
JY
Institute of Biomedical Informatics, Wenzhou Medical College, Wenzhou 325000, China.
Zhao
Fang-Qing
FQ
Bai
Jie
J
Deng
Gang
G
Qin
Song
S
Bao
Qi-Yu
QY
D000220:Adaptation, Biological / Q000235:genetics*; D000595:Amino Acid Sequence; D001413:Bacillus thuringiensis / Q000235:genetics* / Q000378:metabolism; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D001427:Bacterial Toxins / Q000737:chemistry / Q000235:genetics*; D001499:Bayes Theorem; D016000:Cluster Analysis; D016384:Consensus Sequence; D017124:Conserved Sequence; D004731:Endotoxins / Q000737:chemistry / Q000235:genetics*; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006460:Hemolysin Proteins / Q000737:chemistry / Q000235:genetics*; D016013:Likelihood Functions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D012641:Selection, Genetic; D012680:Sensitivity and Specificity; D017386:Sequence Homology, Amino Acid
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis