Gao X G, Maldonado E, Pérez-Montfort R, Garza-Ramos G, de Gómez-Puyou M T, Gómez-Puyou A, Rodríguez-Romero A
Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510 México D. F., Mexico.
Proc Natl Acad Sci U S A. 1999 Aug 31;96(18):10062-7. doi: 10.1073/pnas.96.18.10062.
To gain insight into the mechanisms of enzyme catalysis in organic solvents, the x-ray structure of some monomeric enzymes in organic solvents was determined. However, it remained to be explored whether the structure of oligomeric proteins is also amenable to such analysis. The field acquired new perspectives when it was proposed that the x-ray structure of enzymes in nonaqueous media could reveal binding sites for organic solvents that in principle could represent the starting point for drug design. Here, a crystal of the dimeric enzyme triosephosphate isomerase from the pathogenic parasite Trypanosoma cruzi was soaked and diffracted in hexane and its structure solved at 2-A resolution. Its overall structure and the dimer interface were not altered by hexane. However, there were differences in the orientation of the side chains of several amino acids, including that of the catalytic Glu-168 in one of the monomers. No hexane molecules were detected in the active site or in the dimer interface. However, three hexane molecules were identified on the surface of the protein at sites, which in the native crystal did not have water molecules. The number of water molecules in the hexane structure was higher than in the native crystal. Two hexanes localized at <4 A from residues that form the dimer interface; they were in close proximity to a site that has been considered a potential target for drug design.
为深入了解有机溶剂中酶催化的机制，测定了一些单体酶在有机溶剂中的X射线结构。然而，寡聚蛋白的结构是否也适用于此类分析仍有待探索。当有人提出非水介质中酶的X射线结构可以揭示有机溶剂的结合位点，而这些位点原则上可以作为药物设计的起点时，该领域获得了新的视角。在此，来自致病性寄生虫克氏锥虫的二聚体酶磷酸丙糖异构酶晶体在己烷中浸泡并衍射，其结构在2埃分辨率下解析。己烷并未改变其整体结构和二聚体界面。然而，包括其中一个单体中催化性的Glu-168在内的几个氨基酸侧链的取向存在差异。在活性位点或二聚体界面未检测到己烷分子。然而，在蛋白质表面的一些位点鉴定出三个己烷分子，在天然晶体中这些位点没有水分子。己烷结构中的水分子数量高于天然晶体。两个己烷位于距形成二聚体界面的残基小于4埃处；它们靠近一个被认为是药物设计潜在靶点的位点。
