The 2.5 A X‐ray crystal structure of the acid‐stable proteinase inhibitor from human mucous secretions analysed in its complex with bovine alpha‐chymotrypsin.
The 2.5 A X‐ray crystal structure of the acid‐stable proteinase inhibitor from human mucous secretions analysed in its complex with bovine alpha‐chymotrypsin.
复制标题
分析了来自人类粘液分泌物的酸稳定蛋白酶抑制剂与牛 α-胰凝乳蛋白酶的复合物的 2.5 A X 射线晶体结构。
作者：
M. Grutter;G. Fendrich;R. Huber;W. Bode
生长了牛 α-胰凝乳蛋白酶和重组人粘液蛋白酶抑制剂 (SLPI) 之间形成的复合物的斜方晶体。在区域探测器衍射仪 FAST 上收集分辨率为 2.3 A 的数据。使用胰凝乳蛋白酶作为搜索模型，通过帕特森搜索技术解析了复合物的晶体结构。建模和晶体学细化的循环过程能够确定 SLPI 结构。目前的晶体学 R 值为 0.19。 SLPI 具有类似回旋镖的形状，两个翼由两个结构相似的良好分离的域组成。在每个结构域中，多肽链排列成拉伸的螺旋状。两条内部链形成一个规则的 β 发夹环，并伴有两条由蛋白酶结合片段连接的外部链。每个结构域的多肽片段通过四个二硫桥互连，其连接模式迄今尚未观察到。第二个结构域的反应位点环具有弹性蛋白酶和胰凝乳蛋白酶结合特性。它包含 Leu72I 和 Met73I 之间的可断裂肽键，并且具有与其他丝氨酸蛋白酶蛋白抑制剂中观察到的相似构象。该环的八个残基、两个相邻的发夹环、C 末端片段和 Trp30I 与同源酶直接接触。第一个结构域（可能具有抗胰蛋白酶活性）的结合环由于结晶过程中发生的蛋白水解裂解而紊乱。
Orthorhombic crystals of the complex formed between bovine alpha‐chymotrypsin and a recombinant human mucous proteinase inhibitor (SLPI) were grown. Data to 2.3 A resolution were collected on the area‐detector diffractometer FAST. The crystal structure of the complex was solved by Patterson search techniques using chymotrypsin as a search model. A cyclic procedure of modeling and crystallographic refinement enabled the determination of the SLPI structure. The current crystallographic R‐value is 0.19. SLPI has a boomerang‐like shape with both wings comprising two well separated domains of similar architecture. In each domain the polypeptide chain is arranged like a stretched spiral. Two internal strands form a regular beta‐hairpin loop which is accompanied by two external strands linked by the proteinase binding segment. The polypeptide segment of each domain is interconnected by four disulfide bridges with a connectivity pattern hitherto unobserved. The reactive site loop of the second domain has elastase and chymotrypsin binding properties. It contains the scissile peptide bond between Leu72I and Met73I and has a similar conformation to that observed in other serine proteinase protein inhibitors. Eight residues of this loop, two of the adjacent hairpin loop, the C‐terminal segment and Trp30I are in direct contact with the cognate enzyme. The binding loop of the first domain (probably with anti‐trypsin activity) is disordered due to proteolytic cleavage occurring in the course of crystallization.