The conundrum in enzymatic reactions related to biosynthesis of d-amino acids in bacteria

D-Amino acids (D-AAs) are key components of the peptidoglycan matrix in bacterial cells. Various bacterial species are known to produce D-AAs by using different enzymes, such as highly specific and broad-spectrum racemases. Miyamoto et al. studied the biosynthesis of D-glutamate in the hyperthermophile and anaerobic Gram-negative bacterium, Thermotoga maritima, which does not possess a broad-spectrum racemase. The investigated TM0831 enzyme catalyzes both a D-amino acid aminotransferase reaction producing D-glutamate and an amino acid racemase activity aimed at generating D-aspartate and D-glutamate from the corresponding L-enantiomers. TM0831 represents an example of natural molecular evolution process favoring the enzyme versatility.