Wu Z R, Ebrahimian S, Zawrotny M E, Thornburg L D, Perez-Alvarado G C, Brothers P, Pollack R M, Summers M F
Howard Hughes Medical Institute and Department of Chemistry and Biochemistry, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250.
Science. 1997 Apr 18;276(5311):415-8. doi: 10.1126/science.276.5311.415.
The three-dimensional structure of the enzyme 3-oxo-delta5-steroid isomerase (E.C. 5.3.3.1), a 28-kilodalton symmetrical dimer, was solved by multidimensional heteronuclear magnetic resonance spectroscopy. The two independently folded monomers pack together by means of extensive hydrophobic and electrostatic interactions. Each monomer comprises three alpha helices and a six-strand mixed beta-pleated sheet arranged to form a deep hydrophobic cavity. Catalytically important residues Tyr14 (general acid) and Asp38 (general base) are located near the bottom of the cavity and positioned as expected from mechanistic hypotheses. An unexpected acid group (Asp99) is also located in the active site adjacent to Tyr14, and kinetic and binding studies of the Asp99 to Ala mutant demonstrate that Asp99 contributes to catalysis by stabilizing the intermediate.
3-氧代-δ5-类固醇异构酶（酶编号：E.C. 5.3.3.1）是一种28千道尔顿的对称二聚体，其三维结构通过多维异核磁共振光谱法解析得到。两个独立折叠的单体通过广泛的疏水和静电相互作用聚集在一起。每个单体由三个α螺旋和一个六链混合β折叠片层组成，这些结构排列形成一个深的疏水腔。具有催化重要性的残基Tyr14（广义酸）和Asp38（广义碱）位于腔的底部附近，且位置符合机理假设预期。一个意想不到的酸性基团（Asp99）也位于与Tyr14相邻的活性位点，对Asp99突变为Ala的突变体进行的动力学和结合研究表明，Asp99通过稳定中间体对催化作用有贡献。
