From sequence to function: a new workflow for nitrilase identification

Nitrilases are industrially important biocatalysts due to their ability to degrade nitriles to carboxylic acids and ammonia. In this study, a workflow for simple and fast recovery of nitrilase candidates from metagenomes is presented. For identification of active enzymes, a NADH-coupled high-throughput assay was established. Purification of enzymes could be omitted as the assay is based on crude extract containing the expressed putative nitrilases. In addition, long incubation times were avoided by combining nitrile and NADH conversion in a single reaction. This allowed the direct measurement of nitrile degradation and provided not only insights into substrate spectrum and specificity but also in degradation efficiency. The novel assay was used for investigation of candidate nitrilase-encoding genes. Seventy putative nitrilase-encoding gene and the corresponding deduced protein sequences identified during sequence-based screens of metagenomes derived from nitrile-treated microbial communities were analyzed. Subsequently, the assay was applied to 13 selected candidate genes and proteins. Six of the generated corresponding Escherichia coli clones produced nitrilases that showed activity and one unusual nitrilase was purified and analyzed. The activity of the novel arylacetonitrilase Nit09 exhibited a broad pH range and a high long-term stability. The enzyme showed high activity for arylacetonitriles with a K_M of 1.29 mM and a V_max of 13.85 U/mg protein for phenylacetonitrile. In conclusion, we provided a setup for simple and rapid analysis of putative nitrilase-encoding genes from sequence to function. The suitability was demonstrated by identification, isolation, and characterization of the arylacetonitrilase. KEY POINTS: • A simple and fast high-throughput nitrilase screening was developed. • A set of putative nitrilases was successfully screened with the assay. • A novel arylacetonitrilase was identified, purified, and characterized in detail.