商业食品和l-氨基酸工业依靠生物工程d-氨基酸氧化酶来检测和去除d-氨基酸污染物。然而,由于未能针对限制酶周转的特定动力学步骤,酶产生更快的生物催化剂的生物工程已被证明是困难的,kcat,以及对催化至关重要的循环动力学的理解不足。铜绿假单胞菌d-精氨酸脱氢酶(PaDADH)氧化大多数d-氨基酸,是在l-氨基酸和食品工业中应用的良好候选者。位于PaDADH活性位点口袋入口处的环L2E246残基的侧链潜在地有利于闭合的活性位点构象并在结合时固定底物。本研究采用定点诱变,稳态,和快速反应动力学来产生谷氨酰胺,甘氨酸,和亮氨酸变体,并研究增加产物释放速率是否可以转化为增加的酶周转率。在E246突变为甘氨酸后,d-精氨酸周转率kcat从122增加到500s-1。同样,谷氨酰胺或亮氨酸变体的kcat值增加了2倍.因此,通过选择性地增加PaDADH产品的释放速率,我们为工业应用设计了一种更快的生物催化剂。
Commercial food and l-amino acid industries rely on bioengineered d-amino acid oxidizing enzymes to detect and remove d-amino acid contaminants. However, the bioengineering of enzymes to generate faster biological catalysts has proven difficult as a result of the failure to target specific kinetic steps that limit enzyme turnover, kcat, and the poor understanding of loop dynamics critical for catalysis. Pseudomonas aeruginosa d-arginine dehydrogenase (PaDADH) oxidizes most d-amino acids and is a good candidate for application in the l-amino acid and food industries. The side chain of the loop L2 E246 residue located at the entrance of the PaDADH active site pocket potentially favors the closed active site conformation and secures the substrate upon binding. This study used site-directed mutagenesis, steady-state, and rapid reaction kinetics to generate the glutamine, glycine, and leucine variants and investigate whether increasing the rate of product release could translate to an increased enzyme turnover rate. Upon E246 mutation to glycine, there was an increased rate of d-arginine turnover kcat from 122 to 500 s-1. Likewise, the kcat values increased 2-fold for the glutamine or leucine variants. Thus, we have engineered a faster biocatalyst for industrial applications by selectively increasing the rate of the PaDADH product release.