A Transaminase with Β-Activity from Variovorax Boronicumulans for the Production of Enantiopure Β-Amino Acids

Enantioselective transamination of amino acids is a great challenge in biotechnology as suitable enzymes with wide substrate spectrum are rare. Here, we present a new transaminase from Variovorax boronicumulans (VboTA, Variovorax boronicumulans omega-transaminase) which is specific for beta-amino acids.The amino acid sequence of VboTA is similar to an omega-transaminase from Variovorax paradoxus, for which a crystal-structure is available. This similarity is allowing us to classify VboTA as a fold type 1 omega-transaminase (omega-TA). Although both enzymes have a high sequence similarity (86% identities, 92% positives), there are differences in the active center, which allow VboTA to accept a broader substrate spectrum. Both enzymes have also a different temperature stability and temperature optimum.VboTA deaminates the D-form of aromatic beta-amino acids, such as beta-homophenylalanine and beta-phenylalanine as well as aliphatic beta-amino acids, such as beta-homoalanine and beta-leucine. The optimal reaction conditions turned out to be 32 degrees C and pH 9. Kinetic resolution lead to high enantiomeric excess of 86.6% to >99.9%, depending on the amino donor/acceptor pair. In contrast to many other omega-TAs, VboTA has a broad substrate spectrum and uses both aromatic or aliphatic amino acids. With gamma-amino acids as substrates, VboTA showed no activity at all.