5g09

Publication Abstract from PubMed

omega-Transaminases are enzymes that can introduce an amino group in industrially interesting compounds. We determined crystal structures of two (S)-selective omega-transaminases, one from Arthrobacter sp. (Ars-omegaTA) and one from Bacillus megaterium (BM-omegaTA), which have 95% sequence identity, but somewhat different activity profiles. Substrate-profiling measurements using a range of (R)- and (S)-substrates showed that both enzymes have a preference for substrates with large planar side groups for which the activity of BM-omegaTA is generally somewhat higher. BM-omegaTA has a significantly higher preference for (S)-3,3-dimethyl-2-butylamine than Ars-omegaTA, as well as a more relaxed enantiopreference towards 1-cyclopropylethylamine. The crystal structures showed that, as expected for (S)-selective transaminases, both enzymes have the typical transaminase type I fold, and have spacious active sites to accommodate largish substrates. A structure of BM-omegaTA with bound (R)-alpha-methylbenzylamine explains the enzymes' preference for (S)-substrates. Site-directed mutagenesis experiments revealed that the presence of a tyrosine instead of a cysteine at position 60 increases the relative activities on several small substrates. A structure of Ars-omegaTA with bound L-Ala revealed that the Arg442 side chain has repositioned to bind the L-Ala carboxylate. Compared to the arginine switch residue in other transaminases, Arg442 is shifted by six residues in the amino acid sequence, which appears to be a consequence of extra loops near the active site that narrow the entrance to the active site.

Structural basis of substrate range and enantioselectivity of two (S)-selective omega-transaminases.,van Oosterwijk N, Willies SC, Hekelaar J, Terwisscha van Scheltinga AC, Turner NJ, Dijkstra BW Biochemistry. 2016 Jul 18. PMID:27428867^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.