First characterization of archaeal amino acid racemase
櫻庭, 春彦 Kagawa University
Ohmori, Taketo Osaka Institute of Technology
amino acid racemase
Pyrococcus horikoshii OT-3
broad substrate specificity
A novel amino acid racemase with broad substrate specificity was recently isolated from the hyperthermophilic archaeon Pyrococcus horikoshii OT-3. Characterization of this enzyme has been difficult, however, because the recombinant enzyme is produced mainly as an inclusion body in Escherichia coli. In this study, expression of the recombinant protein into the soluble fraction was markedly improved by co-expression with chaperone molecules. The purified enzyme retained its full activity after incubation at 80°C for at least 2 h in buffer (pH 7-10), making this enzyme the most thermostable amino acid racemase so far known. Besides the nine amino acids containing hydrophobic and aromatic amino acids previously reported (Kawakami et al., Amino acids, 47, 1579-1587, 2015), the enzyme exhibited substantial activity toward Thr (about 42% of relative activity toward Phe) and showed no activity toward Arg, His, Gln, and Asn. The substrate specificity of this enzyme thus differs markedly from those of other known amino acid racemases. In particular, the high reaction rate with Trp and Tyr, in addition to Leu, Met and Phe as substrates is a noteworthy feature of this enzyme. The high reactivity toward Trp and Tyr, as well as extremely high thermostability, is likely a major advantage of using BAR for biochemical conversion of these aromatic amino acids.
Journal of Bioscience and Bioengineering
The Society for Biotechnology|Elsevier
© 2017, The Society for Biotechnology, Japan. All rights reserved. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/.
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