化学
活动站点
异构化
立体化学
基质(水族馆)
纤维二糖
饱和突变
乳果糖
突变
突变体
生物化学
酶
催化作用
纤维素酶
生物
基因
生态学
作者
Lu Wang,Jiali Gu,Wei Zhao,Mingming Wang,Kuan Rei Ng,Xiaomei Lyu,Ruijin Yang
标识
DOI:10.1021/acs.jafc.2c06980
摘要
Enzymatic isomerization of lactose into lactulose via cellobiose 2-epimerase (CE) could provide an eco-friendly route for the industrial production of lactulose, a valuable food prebiotic. However, poor substrate affinity for lactose and preference for epimerization over isomerization hinder this application. Previous studies on CE improvement have focused on random mutagenesis or active site rational design; little is known about the relationship between substrate binding and enzyme efficacy, which was hence the subject of this study. First, residues 372W and 308W were identified as key for disaccharide recognition in CEs based on crystal structure alignment of the N-acetyl-glucosamine 2-epimerase superfamily and site-directed mutation. This binding domain was then reshaped through site saturation mutagenesis, resulting in seven mutants with enhanced isomerization activity. The optimal mutant CsCE/Q371E had significantly enhanced substrate affinity (Km, 269.65 mM vs Km, 417.5 mM), reduced epimerization activity, and 3.3-fold increased isomerization activity over the original CsCE. Molecular dynamics simulation further revealed that substituting Gln-371 with Glu strengthened the hydrogen-bonding network and altered the active site–substrate interactions, increasing the substrate stability and shifting the catalytic direction. This study uncovered new information about the substrate binding region and its mechanisms and impact on CE catalytic performance, paving the way for potential commercial applications.
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