Identification of a novel d‐amino acid aminotransferase involved in d‐glutamate biosynthetic pathways in the hyperthermophile Thermotoga maritima

• Published in: The FEBS journal Vol. 289; no. 19; pp. 5933 - 5946
• Main Authors: Miyamoto, Tetsuya, Moriya, Toshiyuki, Katane, Masumi, Saitoh, Yasuaki, Sekine, Masae, Sakai‐Kato, Kumiko, Oshima, Tairo, Homma, Hiroshi
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.10.2022
• Subjects: Alanine; Alanine racemase; Amino acid racemase; Amino acids; Biosynthesis; d‐amino acid; d‐amino acid aminotransferase; d‐Glutamate; Genomes; Glutamate racemase; Glutamine; Lysine; Peptidoglycans; Thermotoga maritima; Transaminases; d-amino acid; d-Glutamate; Thermotoga maritima; Amino acid racemase; d-amino acid aminotransferase
• ISSN: 1742-464X; 1742-4658
• DOI: 10.1111/febs.16452

The hyperthermophilic bacterium Thermotoga maritima has an atypical peptidoglycan that contains d‐lysine alongside the usual d‐alanine and d‐glutamate. We previously identified a lysine racemase involved in d‐lysine biosynthesis, and this enzyme also possesses alanine racemase activity. However, T. maritima has neither alanine racemase nor glutamate racemase enzymes; hence, the precise biosynthetic pathways of d‐alanine and d‐glutamate remain unclear in T. maritima. In the present study, we identified and characterized a novel d‐amino acid aminotransferase (TM0831) in T. maritima. TM0831 exhibited aminotransferase activity towards 23 d‐amino acids, but did not display activity towards l‐amino acids. It displayed high specific activities towards d‐homoserine and d‐glutamine as amino donors. The most preferred acceptor was 2‐oxoglutarate, followed by glyoxylate. Additionally, TM0831 displayed racemase activity towards four amino acids including aspartate and glutamate. Catalytic efficiency (kcat/Km) for aminotransferase activity was higher than for racemase activity, and pH profiles were distinct between these two activities. To evaluate the functions of TM0831, we constructed a TTHA1643 (encoding glutamate racemase)‐deficient Thermus thermophilus strain (∆TTHA1643) and integrated the TM0831 gene into the genome of ∆TTHA1643. The growth of this TM0831‐integrated strain was promoted compared with ∆TTHA1643 and was restored to almost the same level as that of the wild‐type strain. These results suggest that TM0831 is involved in d‐glutamate production. TM0831 is a novel d‐amino acid aminotransferase with racemase activity that is involved in the production of d‐amino acids in T. maritima. TM0831 is a novel d‐amino acid aminotransferase in Thermotoga maritima. It exhibits broad and unique substrate specificity for aminotransferase activity, and it possesses amino acid racemase activity towards several amino acids. Furthermore, TM0831 recovered the growth of a Glu racemase‐deficient Thermus thermophilus strain. Thus, TM0831 is presumably involved in the production of intracellular d‐Glu.