THE 2.0 A X-RAY CRYSTAL-STRUCTURE OF CHICKEN EGG-WHITE CYSTATIN AND ITS POSSIBLE MODE OF INTERACTION WITH CYSTEINE PROTEINASES
THE 2.0 A X-RAY CRYSTAL-STRUCTURE OF CHICKEN EGG-WHITE CYSTATIN AND ITS POSSIBLE MODE OF INTERACTION WITH CYSTEINE PROTEINASES
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DOI：
10.1002/j.1460-2075.1988.tb03109.x
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发表时间：
1988-08-01
期刊：
影响因子：
11.4
通讯作者：
TURK, V
中科院分区：
文献类型：
--
作者：
BODE, W;ENGH, R;TURK, V
用X射线衍射方法，采用多重同晶置换技术，解析了鸡蛋白色半胱氨酸蛋白酶抑制剂的晶体结构。其结构已用6 - 2.0埃的X射线数据精确到晶体学R值为0.19。该分子主要由直的五圈α-螺旋，五链反平行β-所述折叠片材缠绕并缠绕在所述α-螺旋和附加的部分α-螺旋几何形状。涉及与半胱氨酸蛋白酶结合的从Gln 53 I到Gly 571的“高度保守”区域折叠成紧密的β-发夹环，其在相对侧上侧接氨基末端区段和由类似保守区段Pro 103 I-Trp 104 I组成的第二发夹环。这些环和氨基末端Gly 9 I-Ala 10 I形成楔形“边缘"，这与木瓜蛋白酶的”活性位点裂缝“非常互补。对接实验为半胱氨酸蛋白酶抑制剂与木瓜蛋白酶的相互作用提供了一个独特的模型：半胱氨酸蛋白酶抑制剂的两个发夹卢什与木瓜蛋白酶高度保守的残基Gly 23、Gln 19、Trp 177和Ala 136在反应位点Cys 25附近发生主要的结合作用;结合的半胱氨酸蛋白酶抑制剂的氨基末端片段Gly 9 I-Ala 10 I指向底物亚位点S2，但处于不适当的构象，并且太远而不能被反应位点Cys 25攻击。因此，半胱氨酸蛋白酶和它们的半胱氨酸蛋白酶抑制剂样抑制剂之间的相互作用的机制似乎从根本上不同于丝氨酸蛋白酶和它们的大多数蛋白质抑制剂定义的“标准机制”。
The crystal structure of chicken egg white cystatin has been solved by X-ray diffraction methods using the multiple isomorphous replacement technique. Its structure has been refined to a crystallographic R value of 0.19 using X-ray data between 6 and 2.0.ANG.. The molecule consists mainly of a straight five-turn .alpha.-helix, a five-stranded antiparallel .beta.-pleated sheet which is twisted and wrapped around the .alpha.-helix and an appending segment of partially .alpha.-helical geometry. The ''highly conserved'' region from Gln53I to Gly571 implicated with binding to cysteine proteinases folds into a tight .beta.-hairpin loop which on opposite sides is flanked by the amino-terminal segment and by a second hairpin loop made up of the similarly conserved segment Pro103I-Trp104I. These loops and the amino-terminal Gly9I-Ala10I form a wedge-shaped ''edge'' which is quite complementary to the ''active site cleft'' of papain. Docking experiments suggest a unique model for the interaction of cystatin and papain: according to it both hairpin loos of cystain make major binding interactions with the highly conserved residues Gly23, Gln 19, Trp177 and Ala136 of papain in the neighborhood of the reactive site Cys25; the amino-terminal segment Gly9I-Ala10I of bound cystatin is directed towards the substrate subsite S2, but in an inappropriate conformation and too far away to be attacked by the reactive site Cys25. As a consequence, the mechanism of the interaction between cysteine proteinases and their cystatin-like inhibitors seems to be fundamentally different from the ''standard mechanism'' defined for serine proteinases and most of their protein inhibitors.