Whisstock J C, Skinner R, Carrell R W, Lesk A M
Department of Haematology, Wellcome Trust Centre for the Study of Molecular Mechanisms of Disease, University of Cambridge Clinical School, Hills Road, Cambridge, CB2 2XY, UK.
J Mol Biol. 2000 Jan 21;295(3):651-65. doi: 10.1006/jmbi.1999.3375.
The serpins (SERine Proteinase INhibitors) are a family of proteins with important physiological roles, including but not limited to the inhibition of chymotrypsin-like serine proteinases. The inhibitory mechan- ism involves a large conformational change known as the S-->R (stressed-->relaxed) transition. The largest structural differences occur in a region around the scissile bond called the reactive centre loop: In the native (S) state, the reactive centre is exposed, and is free to interact with proteinases. In inhibitory serpins, in the cleaved (R) state the reactive centre loop forms an additional strand within the beta-sheet. The latent state is an uncleaved state in which the intact reactive centre loop is integrated into the A sheet as in the cleaved form, to give an alternative R state. The serpin structures illustrate detailed control of conformation within a single protein. Serpins are also an unusual family of proteins in which homologues have native states with different folding topologies. Determination of the structures of inhibitory serpins in multiple conformational states permits a detailed analysis of the mechanism of the S-->R transition, and of the way in which a single sequence can form two stabilised states of different topology. Here we compare the conformations of alpha(1)-antitrypsin in native and cleaved states. Many protein conformational changes involve relative motions of large rigid subunits. We determine the rigid subunits of alpha(1)-antitrypsin and analyse the changes in their relative position and orientation. Knowing that the conformational change is initiated by cleavage at the reactive centre, we describe a mechanism of the S-->R transition as a logical sequence of mechanical effects, even though the transition likely proceeds in a concerted manner.
丝氨酸蛋白酶抑制剂（serpins）是一类具有重要生理作用的蛋白质家族，包括但不限于抑制胰凝乳蛋白酶样丝氨酸蛋白酶。其抑制机制涉及一种被称为S→R（紧张态→松弛态）转变的巨大构象变化。最大的结构差异出现在易断裂键周围的一个区域，称为反应中心环：在天然（S）状态下，反应中心是暴露的，可以自由与蛋白酶相互作用。在抑制性丝氨酸蛋白酶抑制剂中，在裂解（R）状态下，反应中心环在β折叠内形成一条额外的链。潜伏态是一种未裂解状态，其中完整的反应中心环如在裂解形式中一样整合到A片中，形成另一种R状态。丝氨酸蛋白酶抑制剂的结构展示了单个蛋白质内构象的精细调控。丝氨酸蛋白酶抑制剂也是一类不同寻常的蛋白质家族，其同源物具有不同折叠拓扑结构的天然状态。确定抑制性丝氨酸蛋白酶抑制剂在多种构象状态下的结构，有助于详细分析S→R转变的机制，以及单个序列如何形成两种不同拓扑结构的稳定状态。在此，我们比较了α1-抗胰蛋白酶在天然状态和裂解状态下的构象。许多蛋白质构象变化涉及大的刚性亚基的相对运动。我们确定了α1-抗胰蛋白酶的刚性亚基，并分析了它们相对位置和方向的变化。鉴于构象变化是由反应中心的裂解引发的，我们将S→R转变的机制描述为一系列合乎逻辑的机械效应序列，尽管这种转变可能是以协同方式进行的。
