Discovery and Characterization of a Novel Thermostable ?-Amino Acid Transaminase from a Meiothermus Strain Isolated in an Icelandic Hot Spring

A Meiothermus strain capable of using ?-phenylalanine for growth is isolated by culture enrichment of samples collected in hot environments and the genome is sequenced showing the presence of 22 putative transaminase (TA) sequences. On the basis of phylogenetic and sequence analysis, a TA termed Ms-TA2 is selected for further studies. The enzyme is successfully produced in Escherichia coli Rosetta(DE3) cells, with 70 mg of pure protein obtained from 1 L culture after purification by affinity chromatography. Ms-TA2 shows high activity toward (S)-?-phenylalanine and other (S)-?-amino acids, as well as a preference for ?-ketoglutarate and aromatic aldehydes as amino acceptors. Moreover, Ms-TA2 is shown to be a thermostable enzyme by maintaining about 60% of the starting activity after 3 h incubation at 50 °C and showing a melting temperature of about 73 °C. Finally, a homology-based structural model of Ms-TA2 is built and key active site interactions for substrate and cofactor binding are analyzed.