Gallagher T, Rozwarski D A, Ernst S R, Hackert M L
Clayton Foundation Biochemical Institute, Department of Chemistry and Biochemistry, University of Texas, Austin 78712.
J Mol Biol. 1993 Mar 20;230(2):516-28. doi: 10.1006/jmbi.1993.1168.
The crystal structure of the pyruvoyl-dependent histidine decarboxylase from Lactobacillus 30a has been refined to an R-value of 0.15 (for the 5.0 to 2.5 A resolution shell) and 0.17 (for the 10.0 to 2.5 A resolution shell). A description of the overall structure is presented, focusing on secondary structure and subunit association. The enzyme is a hexamer of alpha beta subunits. Separate alpha and beta-chains arise from an autocatalytic cleavage reaction between two serine residues, which results in the pyruvoyl cofactor. The central core of the alpha beta subunit is a beta-sandwich which consists of two face-to-face three-stranded antiparallel beta-sheets, flanked by alpha-helices on each side. The beta-sandwich creates a stable fold that allows conformational strain to be introduced across an internal cleavage region between the alpha and beta chains and places the pyruvoyl cofactor in a position for efficient electron withdrawal from the substrate. Three alpha beta subunits are related by a molecular three-fold symmetry axis to form a trimer whose interfaces have complementary surfaces and extensive molecular interactions. Each of the interfaces contains an active site and a solvent channel that leads from the active site to the exterior of the molecule. The trimers are related by a crystallographic two-fold symmetry axis to form the hexamer with an overall dumbbell shape. The interface between trimers has few molecular interactions.
来自乳酸杆菌30a的依赖丙酮酰基的组氨酸脱羧酶的晶体结构已被精修至R值为0.15（对于5.0至2.5埃分辨率壳层）和0.17（对于10.0至2.5埃分辨率壳层）。本文给出了整体结构的描述，重点关注二级结构和亚基缔合。该酶是αβ亚基的六聚体。单独的α链和β链源自两个丝氨酸残基之间的自催化裂解反应，该反应产生丙酮酰基辅因子。αβ亚基的中心核心是一个β-折叠片层，它由两个面对面的三链反平行β-折叠组成，两侧各有α-螺旋。β-折叠片层形成一个稳定的折叠结构，使得构象应变能够在α链和β链之间的内部裂解区域引入，并将丙酮酰基辅因子置于一个能有效从底物中夺取电子的位置。三个αβ亚基通过一个分子三重对称轴相关联，形成一个三聚体，其界面具有互补表面和广泛的分子相互作用。每个界面都包含一个活性位点和一个从活性位点通向分子外部的溶剂通道。三聚体通过一个晶体学二重对称轴相关联，形成具有整体哑铃形状的六聚体。三聚体之间的界面几乎没有分子相互作用。
