Marine Science and Engineering College, Qingdao Agricultural University, Qingdao, 266109, China.
Marine Science and Engineering College, Qingdao Agricultural University, Qingdao, 266109, China; Laboratory for Marine Biology and Biotechnology, Pilot National Laboratory for Marine Science and Technology, Qingdao, China.
Fish Shellfish Immunol. 2019 Oct;93:623-630. doi: 10.1016/j.fsi.2019.08.012. Epub 2019 Aug 7.
Cathepsin S belong to the cathepsin L-like family of cysteine cathepsins. It is well known that Cathepsin S participate in various physiological processes and host immune defense in mammals. However, in teleost fish, the function of cathepsin S is less investigated. In the present study, a cathepsin S homologue (SsCTSS) from the teleost fish black rockfish (Sebastes schlegelii) were identified and examined at expression and functional levels. In silico analysis showed that three domains, including signal peptide, cathepsin propeptide inhibitor I29 domain, and functional domain Pept_C1, were existed in the cathepsin. SsCTSS possesses a peptidase domain with three catalytically essential residues (Cys25, His162, and Asn183). Phylogenetic profiling indicated that SsCTSS are evolutionally close to the cathepsin S of other teleost fish. The expression of SsCTSS in immune-related tissues was upregulated in a time-dependent manner upon bacterial pathogen infection. Purified recombinant SsCTSS (rSsCTSS) exhibited apparent peptidase activity, which was remarkably declined in the presence of the cathepsin inhibitor E-64. rSsCTSS showed strong binding ability to LPS and PGN, the major constituents of the outer membranes of Gram-negative and Gram-positive bacteria, respectively. rSsCTSS also exhibited the capability of agglutination to different bacteria. The knockdown of SsCTSS attenuated the ability of host to eliminate pathogenic bacteria. Taken together, our results suggested that SsCTSS functions as cysteine protease which might be involved in the antibacterial immunity of black rockfish.
组织蛋白酶 S 属于半胱氨酸组织蛋白酶 L 样家族。众所周知，组织蛋白酶 S 参与哺乳动物的各种生理过程和宿主免疫防御。然而，在硬骨鱼类中，组织蛋白酶 S 的功能研究较少。本研究从硬骨鱼类青石斑鱼（Sebastes schlegelii）中鉴定并研究了组织蛋白酶 S 的同源物（SsCTSS），在表达和功能水平上进行了研究。计算机分析表明，该组织蛋白酶存在三个结构域，包括信号肽、组织蛋白酶原抑制剂 I29 结构域和功能域 Pept_C1。SsCTSS 具有肽酶结构域，含有三个催化必需残基（Cys25、His162 和 Asn183）。系统发育分析表明，SsCTSS 与其他硬骨鱼类的组织蛋白酶 S 进化关系密切。免疫相关组织中 SsCTSS 的表达在细菌病原体感染后呈时间依赖性上调。纯化的重组 SsCTSS（rSsCTSS）表现出明显的肽酶活性，而在存在组织蛋白酶抑制剂 E-64 的情况下，其活性显著下降。rSsCTSS 对 LPS 和 PGN 具有很强的结合能力，LPS 和 PGN 分别是革兰氏阴性菌和革兰氏阳性菌外膜的主要成分。rSsCTSS 还表现出对不同细菌的凝集能力。SsCTSS 的敲低削弱了宿主清除病原菌的能力。综上所述，我们的结果表明 SsCTSS 作为半胱氨酸蛋白酶发挥作用，可能参与青石斑鱼的抗菌免疫。
