Acetylornithine aminotransferase TM1785 performs multiple functions in the hyperthermophile Thermotoga maritima

[摘要] The hyperthermophilic bacterium Thermotoga maritima peptidoglycan contains unusual d -lysine alongside typical d -alanine and d -glutamate. We previously identified lysine racemase and threonine dehydratase, but knowledge of d -amino acid metabolism remains limited. Herein, we identified and characterized T .  maritima acetylornithine aminotransferase TM1785. The enzyme was most active towards acetyl- l -ornithine, but also utilized l -glutamate, l -ornithine and acetyl- l -lysine as amino donors, and 2-oxoglutarate was the preferred amino acceptor. TM1785 also displayed racemase activity towards four amino acids and lyase activity towards l -cysteine, but no dehydratase activity towards l -serine, l -threonine or corresponding d -amino acids. Catalytic efficiency ( k cat / K m ) was highest for aminotransferase activity and lowest for racemase activity. TM1785 is a novel acetylornithine aminotransferase associated with l -arginine biosynthesis that possesses two additional distinct activities.

[关键词] acetylornithine aminotransferase;amino acid racemase;cysteine lyase;d-amino acid metabolism;multifunctional enzyme;Thermotoga maritima