Key Residues for Controlling Enantioselectivity of Halohydrin Dehalogenase from Arthrobacter sp Strain AD2, Revealed by Structure-Guided Directed Evolution

作者：Tang, Lixia^*; Zhu, Xuechen; Zheng, Huayu; Jiang, Rongxiang; Elenkov, Maja Majeric

来源：Applied and Environmental Microbiology, 2012, 78(8): 2631-2637.

DOI：10.1128/AEM.06586-11

• AGROBACTERIUM-RADIOBACTER
• KINETIC RESOLUTION
• HALOALCOHOL DEHALOGENASE
• EPOXIDES
• ENZYME
• BINDING
• MUTAGENESIS
• MECHANISM
• SITE

Halohydrin dehalogenase from Agrobacterium radiobacter AD1 (HheC) is a valuable tool in the preparation of R enantiomers of epoxides and beta-substituted alcohols. In contrast, the halohydrin dehalogenase from Arthrobacter sp. AD2 (HheA) shows a low S enantioselectivity toward most aromatic substrates. Here, three amino acids (V136, L141, and N178) located in the two neighboring active-site loops of HheA were proposed to be the key residues for controlling enantioselectivity. They were subjected to saturation mutagenesis aimed at evolving an S-selective enzyme. This led to the selection of two outstanding mutants (the V136Y/L141G and N178A mutants). The double mutant displayed an inverted enantioselectivity (from S enantioselectivity [E-S] = 1.7 to R enantioselectivity [E-R] = 13) toward 2-chloro-1-phenylethanol without compromising enzyme activity. Strikingly, the N178A mutant showed a large enantioselectivity improvement (E-S > 200) and a 5- to 6-fold-enhanced specific activity toward (S)-2-chloro-1-phenylethanol. Further analysis revealed that those mutations produced some interference for the binding of nonfavored enantiomers which could account for the observed enantioselectivities. Our work demonstrated that those three active-site residues are indeed crucial in modulating the enantioselectivity of HheA and that a semirational design strategy has great potential for rapid creation of novel industrial biocatalysts.

• 出版日期2012-4
• 单位电子科技大学