中文摘要：

组织蛋白酶D（cathepsin D,CTSD）是一类存在于溶酶体内的天冬氨酸蛋白内切酶,在蛋白质的水解过程中发挥重要作用.七鳃鳗是低等无颌类脊椎动物,通常依靠吸食宿主鱼类的血肉为生.近年研究发现七鳃鳗（Lampetra japonica）的口腔腺中含有组织蛋白酶D基因（Lamprey-cathepsin D,L-CTSD）.前期实时定量PCR结果推测L-CTSD可能参与了七鳃鳗体内的消化过程.为了深入研究L-CTSD的生物学功能,实验构建了L-CTSD（Leu21-Val396）的原核表达载体p ColdⅠ-L-CTSD,并将其转化至Rosseta blue表达菌中后采用IPTG进行诱导表达.研究发现L-CTSD以包涵体形式表达,通过变性和复性最终获得了可溶性的重组七鳃鳗组织蛋白酶D（recombinat lamprey-cathepsin D,r L-CTSD,43 k Da）.功能实验结果表明：r L-CTSD能够在酸性条件下降解血液中的主要蛋白质成分,如血红蛋白、纤维蛋白原和血清白蛋白等,提示L-CTSD参与了七鳃鳗的消化过程.为深入研究L-CTSD的生物学功能,阐明其在七鳃鳗口腔腺中的作用机制奠定了基础.

英文摘要：

Cathepsin D（CTSD） is an aspartic endoproteinase which is present in the lysosome and plays important roles in the process of protein degradation. Usually, the primitive jawless lampreys live on the blood and flesh of the host fishes. Previous studies have shown that cathepsin D（ lamprey-cathepsin D, L-CTSD） was expressed in the buccal gland of lampreys and might participate in the processes of digestion based on the analysis of real-time-quantitative PCR. In order to study the functions of L-CTSD, pCold I -L-CTSD was constructed and successfully expressed in Rosetta blue cells. After isopropyl beta-D-thiogalactopyranoside （IPTG） induction, recombinant L-CTSD （rL-CTSD） was expressed as the inclusion bodies. The soluble rL-CTSD with the molecular weight of 43 kDa was obtained after denaturation and renaturation. Function studies have shown that rL-CTSD could degrade hemoglobin, fibrinogen and serum alumin in acidic conditions, which are the major protein components in the blood. This suggests that L-CTSD plays important roles in the feeding and digestion processes of lampreys. Thus, the present study will not only reveal the biological functions of L-CTSD, but also illuminate the feeding mechanism of lampreys.