First characterization of an archaeal amino acid racemase with broad substrate specificity from the hyperthermophile Pyrococcus horikoshii OT-3.
A novel amino acid racemase with broad substrate specificity (BAR) 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.
Graduate School of Bioscience and Bioindustry, Tokushima University, 2-1 Minamijosanjima-cho, Tokushima, Tokushima 770-8513, Japan. Electronic address: kawakami@tokushima-u.ac.jp.
Ryushi
R
Kawakami
Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, 2392 Ikenobe, Miki-cho, Kita-gun, Kagawa 761-0795, Japan.
Haruhiko
H
Sakuraba
Department of Biomedical Engineering, Faculty of Engineering, Osaka Institute of Technology, 5-16-1 Omiya, Asahi-ku, Osaka 535-8585, Japan.
Taketo
T
Ohmori
Department of Biomedical Engineering, Faculty of Engineering, Osaka Institute of Technology, 5-16-1 Omiya, Asahi-ku, Osaka 535-8585, Japan.
Toshihisa
T
Ohshima
D000591:Amino Acid Isomerases / Q000378:metabolism*; D000595:Amino Acid Sequence; D057927:Hydrophobic and Hydrophilic Interactions; D043902:Pyrococcus horikoshii / Q000201:enzymology* / Q000502:physiology; D013379:Substrate Specificity; D013696:Temperature
D000591:Amino Acid Isomerases
Amino acid racemase; Broad substrate specificity; Hyperthermophilic archaeon; Kinetics; Pyrococcus horikoshii OT-3