Mechanism of ribonuclease inhibition by ribonuclease inhibitor protein based on the crystal structure of its complex with ribonuclease A
Mechanism of ribonuclease inhibition by ribonuclease inhibitor protein based on the crystal structure of its complex with ribonuclease A
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DOI：
10.1006/jmbi.1996.0694
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发表时间：
1996-12-20
影响因子：
5.6
通讯作者：
Deisenhofer, J
中科院分区：
文献类型：
--
作者：
Kobe, B;Deisenhofer, J
我们描述了核糖核酸酶抑制剂抑制核糖核酸酶的机制，核糖核酸酶抑制剂是一种富含亮氨酸重复序列的蛋白质，基于抑制剂和核糖核酸酶A之间的复合物的晶体结构。通过分子置换确定结构，并在2.5埃分辨率下精修至19.4%的R（cryst）。核糖核酸酶A结合到抑制剂蛋白的凹区，所述凹区包含其平行β-折叠和环。抑制剂覆盖核糖核酸酶活性位点，并直接接触几个活性位点残基。该抑制剂仅部分模拟RNA酶-核苷酸相互作用，并且不利用核糖核酸酶A的pi磷酸结合口袋，其中硫酸根离子保持结合。在络合物形成时掩埋的2550埃（2）的可及表面积可能是极紧密缔合（Ki = 5.9 × 10（-14）M）的主要贡献者之一。这种相互作用主要是静电的，有18个假定的氢键和盐键的高度化学互补性，但形状互补性低于大多数其他蛋白质-蛋白质复合物。核糖核酸酶抑制剂在复合物形成时改变其构象;构象变化是不寻常的，因为它是整个结构的塑性重组，没有任何明显的铰链，反映了抑制剂结构的构象灵活性。晶体结构和其他生物化学研究的相互作用之间有很好的一致性。该结构表明，RI的构象灵活性和一个非常大的接触面积，弥补了较低程度的互补性可能是RI的能力，有力地抑制不同的核糖核酸酶的主要原因。然而，这种抑制作用在两栖类核糖核酸酶和牛精液核糖核酸酶中丧失，两栖类核糖核酸酶取代了大部分与核糖核酸酶A中的结合残基相对应的残基，而牛精液核糖核酸酶通过形成二聚体阻止抑制剂结合。(C)1996年学术出版社
We describe the mechanism of ribonuclease inhibition by ribonuclease inhibitor, a protein built of leucine-rich repeats, based on the crystal structure of the complex between the inhibitor and ribonuclease A. The structure was determined by molecular replacement and refined to an R(cryst) of 19.4% at 2.5 Angstrom resolution. Ribonuclease A binds to the concave region of the inhibitor protein comprising its parallel beta-sheet and loops. The inhibitor covers the ribonuclease active site and directly contacts several active-site residues. The inhibitor only partially mimics the RNase-nucleotide interaction and does not utilize the pi phosphate-binding pocket of ribonuclease A, where a sulfate ion remains bound. The 2550 Angstrom(2) of accessible surface area buried upon complex formation may be one of the major contributors to the extremely tight association (K-i = 5.9 x 10(-14) M). The interaction is predominantly electrostatic; there is a high chemical complementarity with 18 putative hydrogen bonds and salt links, but the shape complementarity is lower than in most other protein-protein complexes. Ribonuclease inhibitor changes its conformation upon complex formation; the conformational change is unusual in that it is a plastic reorganization of the entire structure without any obvious hinge and reflects the conformational flexibility of the structure of the inhibitor. There is a good agreement between the crystal structure and other biochemical studies of the interaction. The structure suggests that the conformational flexibility of RI and an unusually large contact area that compensates for a lower degree of complementarity may be the principal reasons for the ability of RI to potently inhibit diverse ribonucleases. However, the inhibition is lost with amphibian ribonucleases that have substituted most residues corresponding to inhibitor-binding residues in RNase A, and with bovine seminal ribonuclease that prevents inhibitor binding by forming a dimer. (C) 1996 Academic Press Limited