Davies J F, Hostomska Z, Hostomsky Z, Jordan S R, Matthews D A
Agouron Pharmaceuticals, Inc., La Jolla, CA 92037.
Science. 1991 Apr 5;252(5002):88-95. doi: 10.1126/science.1707186.
The crystal structure of the ribonuclease (RNase) H domain of HIV-1 reverse transcriptase (RT) has been determined at a resolution of 2.4 A and refined to a crystallographic R factor of 0.20. The protein folds into a five-stranded mixed beta sheet flanked by an asymmetric distribution of four alpha helices. Two divalent metal cations bind in the active site surrounded by a cluster of four conserved acidic amino acid residues. The overall structure is similar in most respects to the RNase H from Escherichia coli. Structural features characteristic of the retroviral protein suggest how it may interface with the DNA polymerase domain of p66 in the mature RT heterodimer. These features also offer insights into why the isolated RNase H domain is catalytically inactive but when combined in vitro with the isolated p51 domain of RT RNase H activity can be reconstituted. Surprisingly, the peptide bond cleaved by HIV-1 protease near the polymerase-RNase H junction of p66 is completely inaccessible to solvent in the structure reported here. This suggests that the homodimeric p66-p66 precursor of mature RT is asymmetric with one of the two RNase H domains at least partially unfolded.
已确定HIV-1逆转录酶（RT）的核糖核酸酶（RNase）H结构域的晶体结构，分辨率为2.4 Å，并将其精修至晶体学R因子为0.20。该蛋白质折叠成一个五链混合β折叠，两侧是四个α螺旋的不对称分布。两个二价金属阳离子结合在由四个保守酸性氨基酸残基组成的簇所包围的活性位点中。总体结构在大多数方面与来自大肠杆菌的RNase H相似。逆转录病毒蛋白的结构特征表明了它在成熟RT异二聚体中可能如何与p66的DNA聚合酶结构域相互作用。这些特征还为以下问题提供了见解：为什么分离的RNase H结构域没有催化活性，但在体外与RT的分离p51结构域结合时，RNase H活性可以被重建。令人惊讶的是，在此报道的结构中，HIV-1蛋白酶在p66的聚合酶-RNase H连接处附近切割的肽键完全无法接触溶剂。这表明成熟RT的同二聚体p66-p66前体是不对称的，两个RNase H结构域中的一个至少部分未折叠。
