Lukacs C M, Rubin H, Christianson D W
Department of Chemistry, University of Pennsylvania, Philadelphia 19104, USA.
Biochemistry. 1998 Mar 10;37(10):3297-304. doi: 10.1021/bi972359e.
Expressed in a kinetically trapped folding state, a serpin couples the thermodynamic driving force of a massive beta-sheet rearrangement to the inhibition of a target protease. Hence, the serpin-protease interaction is the premier example of a "spring-loaded" protein-protein interaction. Amino acid substitutions in the hinge region of a serpin reactive loop can weaken the molecular spring, which converts the serpin from an inhibitor into a substrate. To probe the molecular basis of this conversion, we report the crystal structure of A349R antichymotrypsin in the reactive loop cleaved state at 2.1 A resolution. This amino acid substitution does not block the beta-sheet rearrangement despite the burial of R349 in the hydrophobic core of the cleaved serpin along with a salt-linked acetate ion. The inhibitory activity of this serpin variant is not obliterated; remarkably, its inhibitory properties are anion-dependent due to the creation of an anion-binding cavity in the cleaved serpin.
丝氨酸蛋白酶抑制剂（serpin）以动力学捕获的折叠状态表达，它将大规模β-折叠重排的热力学驱动力与对靶蛋白酶的抑制作用耦合在一起。因此，丝氨酸蛋白酶抑制剂与蛋白酶的相互作用是“弹簧加载”型蛋白质-蛋白质相互作用的首要例子。丝氨酸蛋白酶抑制剂反应环铰链区的氨基酸取代会削弱分子弹簧，从而将丝氨酸蛋白酶抑制剂从抑制剂转变为底物。为了探究这种转变的分子基础，我们报道了反应环裂解状态下A349R抗胰凝乳蛋白酶的晶体结构，分辨率为2.1埃。尽管R349与一个盐连接的醋酸根离子一起埋入裂解的丝氨酸蛋白酶抑制剂的疏水核心中，但这种氨基酸取代并未阻止β-折叠重排。这种丝氨酸蛋白酶抑制剂变体的抑制活性并未消除；值得注意的是，由于在裂解的丝氨酸蛋白酶抑制剂中形成了一个阴离子结合腔，其抑制特性依赖于阴离子。
