Departamento de Microbiología, Instituto de Fermentaciones Industriales, CSIC, Juan de la Cierva 3, E-28006 Madrid, Spain.
Proteins. 2010 May 15;78(7):1662-76. doi: 10.1002/prot.22684.
p-Coumaric acid decarboxylases (PDCs) catalyze the nonoxidative decarboxylation of hydroxycinnamic acids to generate the corresponding vinyl derivatives. Despite the biotechnological relevance of PDCs in food industry, their catalytic mechanism remains largely unknown. Here, we report insights into the structural basis of catalysis for the homodimeric PDC from Lactobacillus plantarum (LpPDC). The global fold of LpPDC is based on a flattened beta-barrel surrounding an internal cavity. Crystallographic and functional analyses of single-point mutants of residues located within this cavity have permitted identifying a potential substrate-binding pocket and also to provide structural evidences for rearrangements of surface loops so that they can modulate the accessibility to the active site. Finally, combination of the structural and functional data with in silico results enables us to propose a two-step catalytic mechanism for decarboxylation of p-coumaric acid by PDCs where Glu71 is involved in proton transfer, and Tyr18 and Tyr20 are involved in the proper substrate orientation and in the release of the CO(2) product.
对羟基肉桂酸脱羧酶（PDCs）催化羟基肉桂酸的非氧化脱羧反应，生成相应的乙烯基衍生物。尽管 PDC 在食品工业中的生物技术应用具有重要意义，但它们的催化机制在很大程度上仍不清楚。本研究报告了对植物乳杆菌（LpPDC）同源二聚体 PDC 的催化机制的结构基础的深入了解。LpPDC 的整体结构基于围绕内部空腔的扁平β桶。对位于该空腔内的单个残基突变体的晶体学和功能分析，确定了一个潜在的底物结合口袋，并提供了表面环重排的结构证据，从而可以调节对活性位点的可及性。最后，将结构和功能数据与计算机模拟结果相结合，使我们能够提出 PDC 催化对羟基肉桂酸脱羧的两步催化机制，其中Glu71 参与质子转移，Tyr18 和 Tyr20 参与底物的正确取向和 CO2 产物的释放。
