Wolterink-van Loo Suzanne, Levisson Mark, Cabrières Maud C, Franssen Maurice C R, van der Oost John
Laboratory of Microbiology, Wageningen University, Dreijenplein 10, 6703 HB Wageningen, The Netherlands.
Extremophiles. 2008 May;12(3):461-9. doi: 10.1007/s00792-008-0152-z. Epub 2008 Mar 15.
Dihydrodipicolinate synthase (DHDPS) catalyses the first reaction of the (S)-lysine biosynthesis pathway in bacteria and plants. The hypothetical gene for dihydrodipicolinate synthase (dapA) of Thermoanaerobacter tengcongensis was found in a cluster containing several genes of the diaminopimelate lysine-synthesis pathway. The dapA gene was cloned in Escherichia coli, DHDPS was subsequently produced and purified to homogeneity. The T. tengcongensis DHDPS was found to be thermostable (T0.5=3 h at 90 degrees C). The specific condensation of pyruvate and (S)-aspartate-beta -semialdehyde was catalyzed optimally at 80 degrees C at pH 8.0. Enzyme kinetics were determined at 60 degrees C, as close as possible to in vivo conditions. The established kinetic parameters were in the same range as for example E. coli dihydrodipicolinate synthase. The specific activity of the T. tengcongensis DHDPS was relatively high even at 30 degrees C. Like most dihydrodipicolinate synthases known at present, the DHDPS of T. tengcongensis seems to be a tetramer. A structural model reveals that the active site is well conserved. The binding site of the allosteric inhibitor lysine appears not to be conserved, which agrees with the fact that the DHDPS of T. tengcongensis is not inhibited by lysine under physiological conditions.
二氢吡啶二羧酸合酶（DHDPS）催化细菌和植物中（S）-赖氨酸生物合成途径的第一步反应。嗜热栖热放线菌的二氢吡啶二羧酸合酶（dapA）的假定基因是在一个包含二氨基庚二酸赖氨酸合成途径几个基因的基因簇中发现的。dapA基因在大肠杆菌中克隆，随后产生并纯化出均一的DHDPS。发现嗜热栖热放线菌DHDPS具有热稳定性（在90℃时半衰期T0.5 = 3小时）。丙酮酸和（S）-天冬氨酸-β-半醛的特异性缩合在80℃、pH 8.0时催化效果最佳。酶动力学在60℃下测定，尽可能接近体内条件。确定的动力学参数与例如大肠杆菌二氢吡啶二羧酸合酶处于相同范围。嗜热栖热放线菌DHDPS即使在30℃时比活性也相对较高。与目前已知的大多数二氢吡啶二羧酸合酶一样，嗜热栖热放线菌的DHDPS似乎是一种四聚体。结构模型显示活性位点保守性良好。变构抑制剂赖氨酸的结合位点似乎不保守，这与嗜热栖热放线菌的DHDPS在生理条件下不受赖氨酸抑制这一事实相符。
