Enantioselective hydrolysis of epoxides by epoxide hydrolase (EH) is one of the most attractive approaches for the synthesis of chiral epoxides. So far, attempts to develop an efficient epoxide hydrolase -mediated biotransformation have been limited by either the low activity or insufficient enantioselectivity of epoxide hydrolase. In this study, iterative saturation mutagenesis (ISM) of epoxide hydrolase from Agrobacterium radiobacter AD1 (ArEH) was performed for efficient production of (R)-epichlorohydrin. Six amino acid residues, I108, A110, D131, I133, T247, and G245, were selected for site saturation mutagenesis, and a sequential combination of positive mutants using ISM was constructed. Targeted mutagenesis generated five mutants (T247K, I108L, D131S, T247K/I108L, and T247K/I108L/D131S) with improved activity and enantioselectivity. Kinetics analysis showed that the best mutant, T247K/I108L/D131S, exhibited a 4.5-fold higher catalytic efficiency (k cat/K m) value and a 2.1-fold higher enantioselectivity (E value) towards epichlorohydrin than the wild-type (WT) enzyme. Molecular docking computations support the source of notably improved enantioselectivity. In addition, the triple mutant also displayed a significantly enhanced thermostability, with > 8-fold longer half-life at 50 °C than WT. A gram-scale kinetic resolution of (R,S)-epichlorohydrin was performed using T247K/I108L/D131S mutant as biocatalyst, affording a (R)-epichlorohydrin yield of 40.2% (> 99.9% enantiomeric excess) and an average productivity of 1410 g L-1 d-1. The engineered T247K/I108L/D131S variant is a promising biocatalyst for the enzymatic synthesis of (R)-epichlorohydrin.
Submitter: Shu-Ching Ou
Submission Date: March 20, 2019, 4:51 p.m.
Position 108 for ArEH is Phe in the PDB. Here it is changed to Ile.
|Number of data points||144|
|Assays/Quantities/Protocols||Experimental Assay: kcat ; Experimental Assay: Km ; Experimental Assay: kcat/Km ; Experimental Assay: Vmax ; Experimental Assay: Specific Activity ; Experimental Assay: Yield ; Experimental Assay: Enantiomeric Excess ; Experimental Assay: t1/2 at 50 °C ; Experimental Assay: Tm ; Derived Quantity: SD of kcat ; Derived Quantity: SD of Km ; Derived Quantity: SD of kcat/Km ; Derived Quantity: SD of Vmax ; Derived Quantity: SD of Specific Activity ; Derived Quantity: SD of Yield ; Derived Quantity: SD of t1/2 at 50 °C|
|Libraries||Variants for ArEH_Substrate ; Variants for ArEH|