Microbial Genetics Laboratory, Genetic Strains Research Center, National Institute of Genetics 1111 Yata, Mishima, Shizuoka, 411-8540, Japan.
Microbiologyopen. 2012 Sep;1(3):298-310. doi: 10.1002/mbo3.34. Epub 2012 Aug 14.
In bacteria, β-alanine is formed via the action of l-aspartate α-decarboxylase (PanD) which is one of the small class of pyruvoyl-dependent enzymes. The pyruvoyl cofactor in these enzymes is formed via the intramolecular rearrangement of a serine residue in the peptide backbone leading to chain cleavage and formation of the covalently-bound cofactor from the serine residue. This reaction was previously thought to be uncatalysed. Here we show that in Escherichia coli, PanD is activated by the putative acetyltransferase YhhK, subsequently termed PanZ. Activation of PanD both in vivo and in vitro is PanZ-dependent. PanZ binds to PanD, and we demonstrate that a PanZ(N45A) site-directed mutant is unable to enhance cleavage of the proenzyme PanD despite retaining affinity for PanD. This suggests that the putative acetyltransferases domain of PanZ may be responsible for activation to enhance the processing of PanD. Although panD is conserved among most bacteria, the panZ gene is conserved only in E. coli-related enterobacterial species including Shigella, Salmonella, Klebsiella and Yersinia. These bacteria are found predominantly in the gut flora where pantothenate is abundant and regulation of PanD by PanZ allows these organisms to closely regulate production of β-alanine and hence pantothenate in response to metabolic demand.
在细菌中，β-丙氨酸是通过 l-天冬氨酸α-脱羧酶（PanD）的作用形成的，PanD 是一小类依赖 pyruvoyl 的酶之一。这些酶中的 pyruvoyl 辅酶是通过肽骨架中丝氨酸残基的分子内重排形成的，导致链断裂，并从丝氨酸残基形成共价结合的辅酶。以前认为这种反应是无催化的。在这里，我们表明在大肠杆菌中，PanD 被假定的乙酰转移酶 YhhK（随后称为 PanZ）激活。PanD 的体内和体外激活均依赖于 PanZ。PanZ 与 PanD 结合，我们证明 PanZ(N45A)定点突变体尽管保留了与 PanD 的亲和力，但不能增强前体 PanD 的切割。这表明 PanZ 的假定乙酰转移酶结构域可能负责激活以增强 PanD 的加工。尽管 panD 在大多数细菌中都保守，但 panZ 基因仅在与大肠杆菌相关的肠杆菌科物种中保守，包括志贺氏菌、沙门氏菌、克雷伯氏菌和耶尔森氏菌。这些细菌主要存在于肠道菌群中，其中泛酸丰富，PanZ 对 PanD 的调节允许这些生物体根据代谢需求密切调节β-丙氨酸和泛酸的产生。
