Database-driven in silico-identification and characterization of novel aldoxime dehydratases

Aldoxime dehydratases (Oxds) are a unique class of enzymes, which catalyzes the dehydration of aldoximes to nitriles in an aqueous environment. Recently, they gained attention as a catalyst for a green and cyanide-free alternative to established nitrile syntheses, which often require the use of toxic cyanides and harsh reaction conditions. Up to now only thirteen aldoxime dehydratases have been discovered and biochemically characterized. This raised the interest for identifying further Oxds with, e.g., complementary properties in terms of substrate scope. In this study, 16 novel genes, presumably encoding aldoxime dehydratases, were selected by using a commercially available 3DM database based on OxdB, an Oxd from Bacillus sp. OxB-1. Out of 16 proteins, six enzymes with aldoxime dehydratases activity were identified, which differ in their substrate scope and activity. While some novel Oxds showed better performance for aliphatic substrate such as n-octanaloxime compared to the well characterized OxdRE from Rhodococcus sp. N-771, some showed activity for aromatic aldoximes, leading to an overall high usability of these enzymes in organic chemistry. The applicability for organic synthesis was underlined by converting 100 mM n-octanaloxime at a 10 mL scale within 5 h with the novel aldoxime dehydratase OxdHR as whole-cell catalyst (33 mg_bww/mL).