Swairjo M A, Towler E M, Debouck C, Abdel-Meguid S S
Department of Structural Biology and Molecular Biology, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406, USA.
Biochemistry. 1998 Aug 4;37(31):10928-36. doi: 10.1021/bi980784h.
The structural basis of ligand specificity in human immunodeficiency virus (HIV) protease has been investigated by determining the crystal structures of three chimeric HIV proteases complexed with SB203386, a tripeptide analogue inhibitor. The chimeras are constructed by substituting amino acid residues in the HIV type 1 (HIV-1) protease sequence with the corresponding residues from HIV type 2 (HIV-2) in the region spanning residues 31-37 and in the active site cavity. SB203386 is a potent inhibitor of HIV-1 protease (Ki = 18 nM) but has a decreased affinity for HIV-2 protease (Ki = 1280 nM). Crystallographic analysis reveals that substitution of residues 31-37 (30's loop) with those of HIV-2 protease renders the chimera similar to HIV-2 protease in both the inhibitor binding affinity and mode of binding (two inhibitor molecules per protease dimer). However, further substitution of active site residues 47 and 82 has a compensatory effect which restores the HIV-1-like inhibitor binding mode (one inhibitor molecule in the center of the protease active site) and partially restores the affinity. Comparison of the three chimeric protease structures with those of HIV-1 and SIV proteases complexed with the same inhibitor reveals structural changes in the flap regions and the 80's loops, as well as changes in the dimensions of the active site cavity. The study provides structural evidence of the role of the 30's loop in conferring inhibitor specificity in HIV proteases.
通过测定三种与三肽类似物抑制剂SB203386复合的嵌合型人类免疫缺陷病毒（HIV）蛋白酶的晶体结构，对HIV蛋白酶中配体特异性的结构基础进行了研究。这些嵌合体是通过在1型HIV（HIV-1）蛋白酶序列中，用2型HIV（HIV-2）在31 - 37位残基区域以及活性位点腔中的相应残基替换氨基酸残基构建而成。SB203386是HIV-1蛋白酶的有效抑制剂（Ki = 18 nM），但对HIV-2蛋白酶的亲和力降低（Ki = 1280 nM）。晶体学分析表明，用HIV-2蛋白酶的残基替换31 - 37位残基（30's环），使嵌合体在抑制剂结合亲和力和结合模式（每个蛋白酶二聚体有两个抑制剂分子）上与HIV-2蛋白酶相似。然而，进一步替换活性位点残基47和82具有补偿作用，恢复了类似HIV-1的抑制剂结合模式（一个抑制剂分子位于蛋白酶活性位点中心）并部分恢复了亲和力。将三种嵌合蛋白酶结构与结合相同抑制剂的HIV-1和SIV蛋白酶结构进行比较，揭示了侧翼区域和80's环的结构变化，以及活性位点腔尺寸的变化。该研究提供了30's环在赋予HIV蛋白酶抑制剂特异性中作用的结构证据。
