Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, PR China.
Dev Comp Immunol. 2010 Dec;34(12):1237-41. doi: 10.1016/j.dci.2010.07.008. Epub 2010 Aug 12.
Cystatins form a large family of cysteine protease inhibitors found in a wide arrange of organisms. Studies have indicated that mammalian cystatins play important roles under both physiological and pathological conditions. However, much less is known about fish cystatins. In this report, we described the identification and analysis of a cystatin B homologue, SmCytB, from turbot Scophthalmus maximus. The open reading frame of SmCytB is 300bp, which encodes a 99-residue protein that shares high levels of sequence identities with the cystatin B of a number of fish species and contains the conserved cysteine protease inhibitor motif of cystatin B. Constitutive expression of SmCytB is high in muscle, brain, heart and liver, and low in spleen, blood, gill and kidney. Bacterial infection upregulates SmCytB expression in kidney, spleen, liver and brain but not in muscle or heart. Functional analysis showed that recombinant SmCytB purified from Escherichia coli exhibits apparent cysteine protease inhibitor activity. Transient overexpression of SmCytB in head kidney macrophages enhances macrophage bactericidal activity probably through a nitric oxide-independent mechanism. These results indicate that SmCytB is involved in the immune defense of turbot against bacterial infection.
组织蛋白酶抑制剂构成了一个庞大的半胱氨酸蛋白酶抑制剂家族，存在于多种生物中。研究表明，哺乳动物组织蛋白酶抑制剂在生理和病理条件下都发挥着重要作用。然而，关于鱼类组织蛋白酶抑制剂的了解要少得多。在本报告中，我们描述了从大菱鲆（Scophthalmus maximus）中鉴定和分析一种组织蛋白酶 B 同源物 SmCytB 的情况。SmCytB 的开放阅读框为 300bp，编码一个 99 个氨基酸的蛋白质，与许多鱼类的组织蛋白酶 B 具有高度的序列同一性，并含有组织蛋白酶 B 的保守半胱氨酸蛋白酶抑制剂基序。SmCytB 在肌肉、大脑、心脏和肝脏中的组成型表达水平较高，在脾脏、血液、鳃和肾脏中的表达水平较低。细菌感染会在上皮组织中的肾脏、脾脏、肝脏和大脑中上调 SmCytB 的表达，但不会在肌肉或心脏中上调。功能分析表明，从大肠杆菌中纯化的重组 SmCytB 表现出明显的半胱氨酸蛋白酶抑制剂活性。瞬时过表达 SmCytB 在上皮组织中的巨噬细胞中增强了巨噬细胞的杀菌活性，可能是通过一种不依赖于一氧化氮的机制。这些结果表明 SmCytB 参与了大菱鲆抵抗细菌感染的免疫防御。
