Nitrile Reductase from Geobacillus kaustophilus: A Potential Catalyst for a New Nitrile Biotransformation Reaction

The cloning, expression and characterization of a nitrile reductase (NRed) from the thermophile Geobacillus kaustophilus is reported. The enzyme shows a 12-fold increase in activity in response to a temperature change from 25 °C to 65 °C. The substrate scope regarding its biocatalytic applicability was investigated by testing a range of common nitriles. The narrow substrate range observed for the wild-type enzyme prompted the rational design of GkNRed active site mutants based on a previously published homology model from Bacillus subtilis. The activities of the mutants and the wild-type enzyme were investigated in their structure-function relationship regarding the natural substrate 7-cyano-7-deazaguanine (preQ0) as well as a range of synthesized preQ0-like substrate structures. A distinct dependence of the wild-type enzyme activity on specific structural modifications of the natural substrate was observed. Two non-natural nitriles derived from preQ0 could be reduced to their corresponding amino compounds.