PLP-dependent enzymes catalyze a plethora of chemical reactions affecting diverse physiological functions. Here we report the structural determinants of the reaction mechanism in a Group II PLP-dependent decarboxylase by assigning two early intermediates. The in-crystallo complexes of the PLP bound form, and the Dunathan and quinonoid intermediates, allowed direct observation of the active site interactions. The structures reveal that a subtle rearrangement of a conserved Arg residue in concert with a water-mediated interaction with the carboxylate of the Dunathan intermediate, appears to directly stabilize the alignment and facilitate the release of CO₂ to yield the quinonoid. Modeling indicates that the conformational change of a dynamic catalytic loop to a closed form controls a conserved network of hydrogen bond interactions between catalytic residues to protonate the quinonoid. Our results provide a structural framework to elucidate mechanistic roles of residues that govern reaction specificity and catalysis in PLP-dependent decarboxylation.

PLP依赖性酶催化多种化学反应，影响多种生理功能。在这里，我们通过分配两个早期的中间体报告了第二类PLP依赖的脱羧酶中反应机理的结构决定因素。的在-crystallo络合物PLP结合形式的，并且Dunathan和醌型中间体，所允许的活性位点的相互作用的直接观察。结构表明保守的Arg残基的细微重排与水与Dunathan中间体的羧酸盐的相互作用介导，似乎可以直接稳定排列并促进CO ₂的释放产生醌类。建模表明，动态催化环向闭合形式的构象变化控制了催化残基之间的氢键相互作用的保守网络，以使醌类质子化。我们的结果提供了一个结构框架，阐明了在PLP依赖性脱羧反应中控制反应特异性和催化作用的残基的机械作用。