Wu Jin-Yu, Zhao Fang-Qing, Bai Jie, Deng Gang, Qin Song, Bao Qi-Yu
Institute of Biomedical Informatics, Wenzhou Medical College, Wenzhou 325000, China.
Genomics Proteomics Bioinformatics. 2007 May;5(2):102-10. doi: 10.1016/S1672-0229(07)60020-5.
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.
cry基因家族是在苏云金芽孢杆菌生长指数后期产生的，它是一个庞大且仍在不断增长的同源基因家族，其中每个基因编码一种仅对一种或几种昆虫具有强特异性活性的蛋白质。广泛的研究大多集中在Cry蛋白的结构和功能关系上，并揭示了几个对靶标识别和受体附着很重要的残基或结构域。在本研究中，我们采用最大似然法来检测Cry蛋白中适应性进化的证据，并鉴定出24个正选择残基，它们均位于结构域II或III中。结合诱变研究的已知数据，在分子水平上，这些残基中的大多数对昆虫特异性的确定有很大贡献。我们推测，驱动Cry蛋白多样化的潜在压力可能是为了适应δ-内毒素与目标昆虫之间的“军备竞赛”，或者扩大其靶标谱，从而导致功能分化。被确定为正选择的位点将为进一步对Cry蛋白进行结构和功能分析提供靶点。
