Acetylornithine aminotransferase TM1785 performs multiple functions in the hyperthermophile Thermotoga maritima

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.

极端嗜热细菌海栖热袍菌（Thermotoga maritima）的肽聚糖除了含有典型的D -丙氨酸和D -谷氨酸外，还含有不寻常的D -赖氨酸。我们之前鉴定出了赖氨酸消旋酶和苏氨酸脱水酶，但对D -氨基酸代谢的了解仍然有限。在此，我们鉴定并表征了海栖热袍菌的乙酰鸟氨酸氨基转移酶TM1785。该酶对乙酰 - L -鸟氨酸活性最高，但也利用L -谷氨酸、L -鸟氨酸和乙酰 - L -赖氨酸作为氨基供体，并且2 - 酮戊二酸是首选的氨基受体。TM1785还对四种氨基酸显示消旋酶活性，对L -半胱氨酸显示裂解酶活性，但对L -丝氨酸、L -苏氨酸或相应的D -氨基酸没有脱水酶活性。催化效率（kcat / Km）对于氨基转移酶活性最高，对于消旋酶活性最低。TM1785是一种与L -精氨酸生物合成相关的新型乙酰鸟氨酸氨基转移酶，它还具有另外两种不同的活性。