Filipek Renata, Rzychon Malgorzata, Oleksy Aneta, Gruca Milosz, Dubin Adam, Potempa Jan, Bochtler Matthias
International Institute of Molecular and Cell Biology, ul Trojdena 4, 02-109 Warsaw, Poland.
J Biol Chem. 2003 Oct 17;278(42):40959-66. doi: 10.1074/jbc.M302926200. Epub 2003 Jul 21.
Staphostatins are the endogenous inhibitors of the major secreted cysteine proteases of Staphylococcus aureus, the staphopains. Our recent crystal structure of staphostatin B has shown that this inhibitor forms a mixed, eight-stranded beta-barrel with statistically significant similarity to lipocalins, but not to cystatins. We now present the 1.8-A crystal structure of staphostatin B in complex with an inactive mutant of its target protease. The complex is held together through extensive interactions and buries a total surface area of 2300 A2. Unexpectedly for a cysteine protease inhibitor, staphostatin B binds to staphopain B in an almost substrate-like manner. The inhibitor polypeptide chain runs through the protease active site cleft in the forward direction, with residues IG-TS in P2 to P2' positions. Both in the free and complexed forms, the P1 glycine residue of the inhibitor is in a main chain conformation only accessible to glycines. Mutations in this residue lead to a loss of affinity of the inhibitor for protease and convert the inhibitor into a substrate.
葡萄球菌抑制素是金黄色葡萄球菌主要分泌的半胱氨酸蛋白酶（葡萄球菌蛋白酶）的内源性抑制剂。我们最近解析的葡萄球菌抑制素B的晶体结构表明，这种抑制剂形成了一种混合的八链β桶结构，与脂质运载蛋白在统计学上具有显著相似性，但与胱抑素不同。我们现在展示了葡萄球菌抑制素B与其靶蛋白酶的无活性突变体形成的复合物的1.8埃晶体结构。该复合物通过广泛的相互作用结合在一起，掩埋的总表面积为2300埃²。对于一种半胱氨酸蛋白酶抑制剂而言出乎意料的是，葡萄球菌抑制素B以一种几乎类似底物的方式与葡萄球菌蛋白酶B结合。抑制剂多肽链向前穿过蛋白酶活性位点裂隙，P2至P2'位置的残基为IG-TS。无论是游离形式还是复合形式，抑制剂的P1甘氨酸残基都处于仅甘氨酸可及的主链构象。该残基的突变导致抑制剂对蛋白酶的亲和力丧失，并将抑制剂转化为底物。
