Ala/Ser Racemase From P. horikoshii
Ohshida, Tatsuya Kagawa University
櫻庭, 春彦 Kagawa University
Pyrococcus horikoshii OT-3
We recently identified and characterized a novel broad substrate specificity amino acid racemase (BAR) from the hyperthermophilic archaeon Pyrococcus horikoshii OT-3. Three genes, PH0782, PH1423, and PH1501, encoding homologs exhibiting about 45% sequence identity with BAR were present in the P. horikoshii genome. In this study, we detected pyridoxal 5'-phosphate (PLP)-dependent amino acid racemase activity in the protein encoded by PH0782. The enzyme showed activity toward Ala, Ser, Thr, and Val, but the catalytic efficiency with Thr or Val was much lower than with Ala or Ser. The enzyme was therefore designated Ala/Ser racemase (ASR). Like BAR, ASR was highly stable at high temperatures and over a wide range of pHs, though its hexameric structure differed from the dimeric structure of BAR. No activity was detected in K291A or D234A ASR mutants. This suggests that, as in Ile 2-epimerase (ILEP) from Lactobacillus buchneri JCM1115, these residues are involved in Schiff base formation and substrate interaction, respectively. Unlike BAR, enhanced ASR activity was not detected in P. horikoshii cells cultivated in the presence of D-Ala or D-Ser. This is the first description of a PLP-dependent fold type I ASR in archaea.
Frontiers in Microbiology
Frontiers Media S.A.
© 2018 Kawakami, Ohshida, Sakuraba and Ohshima. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY)( https://creativecommons.org/licenses/by/4.0/). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
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