The First Thermophilic α-Oxoamine Synthase Family Enzyme That Has Activities of 2-Amino-3-ketobutyrate CoA Ligase and 7-Keto-8-aminopelargonic Acid Synthase: Cloning and Overexpression of the Gene from an Extreme Thermophile,<i>Thermus thermophilus</i>, and Characterization of Its Gene Product
作者:Takaaki KUBOTA、Jyunpei SHIMONO、Chie KANAMEDA、Yoshikazu IZUMI
DOI:10.1271/bbb.70438
日期:2007.12.23
The first thermophilic α-oxoamine synthase family enzyme was identified. The gene (ORF TTHA1582), which is annotated to code putative α-oxoamine synthase family enzymes, 7-keto-8-aminopelargonic acid (KAPA) synthase (BioF, 8-amino-7-oxononanoate synthase, EC 2.3.1.47) and 2-amino-3-ketobutyrate CoA ligase (KBL, EC 2.3.1.29), in a genomic database, was cloned from an extreme thermophile, Thermus thermophilus, and overexpressed in Escherichia coli. The recombinant TTHA1582 protein was purified and characterized. It exhibited activity of BioF, which catalyzes the condensation of pimeloyl-CoA and l-alanine to produce a biotin intermediate KAPA, CoASH, and CO2 with pyridoxal 5′-phosphate as a cofactor. The protein is a dimer with a subunit of 43 kDa that shows an amino acid sequence identity of 35% with E. coli BioF. The optimum temperature and pH were about 70 °C and about 6.0. The enzyme showed high thermostability at temperatures of up to 70 °C for 1 h, and a half-life of 1 h at 80 °C. Thus the TTHA1582 protein was found to have the highest optimum temperature and thermostablility of the α-oxoamine synthase family enzymes so far reported. Substrate specificity experiments revealed that it was also able to catalyze the KBL reaction, which used acetyl-CoA and glycine as substrates, and that enzyme activity was seen with the following combinations of substrates: acetyl-CoA and glycine, l-alanine, or l-serine; pimeloyl-CoA and l-alanine, glycine, or l-serine; palmitoyl-CoA and l-alanine. This suggests that the recombinant TTHA1582 protein has broad substrate specificity, unlike the reported mesophilic enzymes of the α-oxoamine synthase family.
鉴定出第一个嗜热 α-氧代胺合酶家族酶。基因 (ORF TTHA1582),注释为编码推定的 α-氧代胺合酶家族酶、7-酮-8-氨基壬酸 (KAPA) 合酶(BioF,8-氨基-7-氧代壬酸合酶,EC 2.3.1.47)和2-氨基-3-酮丁酸 CoA 连接酶(KBL、EC 2.3.1.29),在基因组数据库中,是从极端嗜热菌,嗜热栖热菌中克隆出来的,并在大肠杆菌中过表达。对重组 TTHA1582 蛋白进行纯化和表征。它具有 BioF 活性,可催化庚二酰辅酶 A 和 L-丙氨酸缩合,以 5'-磷酸吡哆醛为辅因子,生成生物素中间体 KAPA、CoASH 和 CO2。该蛋白是亚基为 43 kDa 的二聚体,与大肠杆菌 BioF 的氨基酸序列同一性为 35%。最适温度和pH值约为70℃和6.0左右。该酶在高达 70 °C 的温度下表现出高热稳定性,持续 1 小时,在 80 °C 时半衰期为 1 小时。因此,发现TTHA1582蛋白在迄今为止报道的α-氧代胺合酶家族中具有最高的最适温度和热稳定性。底物特异性实验表明,它还能够催化 KBL 反应,该反应使用乙酰辅酶 A 和甘氨酸作为底物,并且通过以下底物组合观察到酶活性:乙酰辅酶A 和甘氨酸、L-丙氨酸或 L -丝氨酸;庚二酰辅酶A和L-丙氨酸、甘氨酸或L-丝氨酸;棕榈酰辅酶A和L-丙氨酸。这表明重组 TTHA1582 蛋白具有广泛的底物特异性,与报道的 α-氧代胺合酶家族的嗜温酶不同。