O-Acetyl-L-homoserine sulfhydrylase from Thermotoga maritima has five enzyme activities

We previously demonstrated that the hyperthermophilic bacterium Thermotoga maritima has unique metabolic pathways for D- and L-amino acids. In the present study, we characterized O-acetyl-L-homoserine sulfhydrylase (MetY) TM0882 associated with L-methionine biosynthesis. MetY catalyzes the production of L-homocysteine from O-acetyl-L-homoserine and hydrogen sulfide. We found that TM0882 also possesses β-lyase, racemase/α-epimerase, aminotransferase, and decarboxylase activities. This enzyme displayed L-cysteine β-lyase activity as well as racemase/α-epimerase activity toward glutamate and threonine. Furthermore, TM0882 exhibited aminotransferase and L-aspartate 4-decarboxylase activities. Catalytic efficiency (k_cat/K_m) for β-lyase activity was highest among the four additional activities. TM0882 is therefore a multifunctional enzyme possessing four different activities in addition to sulfhydrylase activity.