Inhibitory mechanism of a cross-class serpin, the squamous cell carcinoma antigen 1
Inhibitory mechanism of a cross-class serpin, the squamous cell carcinoma antigen 1
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DOI：
10.1074/jbc.m307741200
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发表时间：
2003-11-14
影响因子：
4.8
通讯作者：
Izuhara, K
中科院分区：
文献类型：
--
作者：
Masumoto, K;Sakata, Y;Izuhara, K
鳞状细胞癌抗原（SCCA） 1及其同源分子SCCA2属于卵清蛋白-蛇形蛋白家族。虽然SCCA2抑制丝氨酸蛋白酶如组织蛋白酶G和肥大细胞乳糜酶，但SCCA1靶向半胱氨酸蛋白酶如组织蛋白酶S、K、L和木瓜蛋白酶。因此，SCCA1被称为跨类蛇形蛋白。对标准蛇形蛋白的抑制机制进行了较好的表征；它们使用类似自杀底物的抑制机制，在此过程中，酰基酶中间体通过共价键形成，该复合物对水解是稳定的。然而，跨类蛇形蛋白的抑制机制尚不清楚。在本文中，我们分析了SCCA1对半胱氨酸蛋白酶木瓜蛋白酶的抑制机制。SCCA1在其反应位点环上与木瓜蛋白酶相互作用，然后作为标准蛇形蛋白酶被切割。然而，凝胶过滤分析表明，与其他蛇形蛋白相比，SCCA1不与木瓜蛋白酶形成共价复合物。与SCCA1的相互作用可能通过诱导构象变化严重损害了木瓜蛋白酶的活性。根据自杀底物样抑制机制，SCCA1完全抑制了木瓜蛋白酶活性的降低，但仍然存在；然而，当所有完整的SCCA1被切割时，木瓜蛋白酶的蛋白酶活性在受损水平上恢复。这些结果表明，SCCA1的抑制机制在蛇形蛋白超家族中是独特的，因为SCCA1通过两种方式发挥其抑制活性，一种是不形成共价复合物的自杀底物机制，另一种是对蛋白酶的催化活性造成不可逆的损害。
The squamous cell carcinoma antigen (SCCA) 1 and its homologous molecule, SCCA2, belong to the ovalbumin-serpin family. Although SCCA2 inhibits serine proteinases such as cathepsin G and mast cell chymase, SCCA1 targets cysteine proteinases such as cathepsin S, K, L, and papain. SCCA1 is therefore called a cross-class serpin. The inhibitory mechanism of the standard serpins is well characterized; those use a suicide substrate-like inhibitory mechanism during which an acyl-enzyme intermediate by a covalent bond is formed, and this complex is stable against hydrolysis. However, the inhibitory mechanism of cross-class serpins remains unresolved. In this article, we analyzed the inhibitory mechanism of SCCA1 on a cysteine proteinase, papain. SCCA1 interacted with papain at its reactive site loop, which was then cleaved, as the standard serpins. However, gel-filtration analyses showed that SCCA1 did not form a covalent complex with papain, in contrast to other serpins. Interaction with SCCA1 severely impaired the proteinase activity of papain, probably by inducing conformational change. The decreased, but still existing, proteinase activity of papain was completely inhibited by SCCA1 according to the suicide substrate-like inhibitory mechanism; however, papain recovered its proteinase activity with the compromised level, when all of intact SCCA1 was cleaved. These results suggest that the inhibitory mechanism of SCCA1 is unique among the serpin superfamily in that SCCA1 performs its inhibitory activity in two ways, contributing the suicide substrate-like mechanism without formation of a covalent complex and causing irreversible impairment of the catalytic activity of a proteinase.