华支睾吸虫组织蛋白酶Cathepsin L1样基因全长序列的克隆和生物信息学分析

目的预测华支睾吸虫全长cDNA质粒文库中cs002d09号EST序列的结构和功能特征及编码蛋白的应用前景。方法利用NCBI和ExPaSy等生物信息学网站在线分析工具和Vector NTIsuite及PcGene等软件包，分析华支睾吸虫全长cDNA质粒文库中cs002d09号EST序列及其编码蛋白的理化性质、结构与功能特征。结果BLASTx分析该ESF序列是组织蛋白酶Cathepsin L1的同源基因，全序列长为1458bp，包含完整的编码区80～1191，编码371个氨基酸，前18个氨基酸是分泌信号肽，蛋白的理化性质较稳定。该蛋白有2个空间构象相对独立功能域：N端的抑制功能域和C端的活性功能域，抑制功能域含有3个线性B细胞抗原表位，同源性较低；C端活性功能域同源性较高，Cys177，His318和Asn338组成催化中心，位于底物结合裂缝的底部。结论华支睾吸虫Cathepsin Ll基因与多个物种的Cathepsin L1基因同源，编码蛋白可能是重要的虫体分泌排泄抗原成分，在华支睾吸虫病的免疫诊断和疫苗研究方面有较好的应用前景。

Cloning and bioinformatic analysis of cathepsin Ll-like full-length gene from Clonorchis sinensis

Objective To predict the structural and functional characteristics of cs002d09 EST from Clonorchis sinensis full-length cDNA plasmid library and its prospects of application. Methods Utilizing the analysis tools provided by NCBI（http：//www. ncbi. nlm. nih. gov/）, ExPaSy （http：//www. expasy, org/） and the complicated bioinformatics software packages, such as PcGene, Vector NTI suite 8.0 were used to identify a EST clone （NO. cs002d09） from the C. sinensis full length cI）NA plasmid library and analyze its coding region and the physico-chemical properties and structural and functional characteristics of the deduced protein. Results The EST was predicted as a homologue of cathepsin L1, with 1 458 bp in length and a complete coding region 80-1 191 for 371 amino acids. The protein contained a secretory signal peptide of 18 amino acids residues in the N terminus, with stable physico chemical property. The protein was composed of two spatially relatively independent domains, inhibitory domain （67-127） in the N segment and active catalytic domain in the C-terminal segment. Contradiction to the conserved C-terminal functional domain with a substrate-binding cleft in which bottom lies three key amino acids Cyst77, His318 and Asn328 consisting the catalytic sites, the inhibitory domain cov- ered the substrate cleft and was of much lower homology and contained three linear B cell epitopes. Conclusion C. sinensis cathepsin IA is homologous with cathepsin L1 from other species and is probably a component of excretory secretory antigen and maybe a promising candidate for vaccine and immunodiagnosis for clonorchiasis.