Development of a Novel Biocatalyst for the Resolution of rac-Pantolactone

Abstract

A novel L-pantolactone hydrolase, Lph, from Agrobacterium tumefaciens Lu681 was characterized, which stereospecifically hydrolyses L-pantolactone to L-pantoic acid yielding D-pantolactone with > 95% enantiomeric excess. The enzyme was found to be a 30 kDa-Zn2+-hydrolase with a Km for L-pantolactone of 7 mM and a Vmax of 30 U/mg. The corresponding lph gene was identified as an 807 bp ORF and cloned into E. coli. It was overexpressed under control of Ptac and Prha yielding enzyme activities of up to 600 U/g dry weight. Resolution of D,L-pantolactone in repeated batches with isolated Lph and enzyme recovery by membrane filtration gave D-pantolactone with 50% yield and 90-95% ee over 6 days. Covalent immobilization to EupergitC led to a stable biocatalyst easy to handle in a repeated batch production of D-pantolactone. Further improvements in the activity of Lph were achieved by directed evolution of the enzyme. Activities of mutants F62S, K197D and F100L were increased 2.3, 1.7, and 1.5 fold, respectively.