Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, China.
College of Life Sciences, Zhejiang University, Hangzhou, China.
J Bacteriol. 2019 Mar 13;201(7). doi: 10.1128/JB.00665-18. Print 2019 Apr 1.
Picolinic acid (PA), a typical C-2-carboxylated pyridine derivative, is a metabolite of l-tryptophan and many other aromatic compounds in mammalian and microbial cells. Microorganisms can degrade and utilize PA for growth. However, the precise mechanism of PA metabolism remains unknown. strain JQ135 utilizes PA as its carbon and nitrogen source for growth. In this study, we screened a 6-hydroxypicolinic acid (6HPA) degradation-deficient mutant through random transposon mutagenesis. The mutant hydroxylated 6HPA into an intermediate, identified as 3,6-dihydroxypicolinic acid (3,6DHPA), with no further degradation. A novel decarboxylase, PicC, was identified to be responsible for the decarboxylation of 3,6DHPA to 2,5-dihydroxypyridine. Although, PicC belonged to the amidohydrolase 2 family, it shows low similarity (<45%) compared to other reported amidohydrolase 2 family decarboxylases. Moreover, PicC was found to form a monophyletic group in the phylogenetic tree constructed using PicC and related proteins. Further, the genetic deletion and complementation results demonstrated that was essential for PA degradation. The PicC was Zn-dependent nonoxidative decarboxylase that can specifically catalyze the irreversible decarboxylation of 3,6DHPA to 2,5-dihydroxypyridine. The and toward 3,6DHPA were observed to be 13.44 μM and 4.77 s, respectively. Site-directed mutagenesis showed that His163 and His216 were essential for PicC activity. This study provides new insights into the microbial metabolism of PA at molecular level. Picolinic acid is a natural toxic pyridine derived from l-tryptophan metabolism and other aromatic compounds in mammalian and microbial cells. Microorganisms can degrade and utilize picolinic acid for their growth, and thus a microbial degradation pathway of picolinic acid has been proposed. Picolinic acid is converted into 6-hydroxypicolinic acid, 3,6-dihydroxypicolinic acid, and 2,5-dihydroxypyridine in turn. However, there was no physiological and genetic validation for this pathway. This study demonstrated that 3,6-dihydroxypicolinic acid was an intermediate in picolinic acid catabolism and further identified and characterized a novel amidohydrolase 2 family decarboxylase PicC. PicC was also shown to catalyze the decarboxylation of 3,6-dihydroxypicolinic acid into 2,5-dihydroxypyridine. This study provides a basis for understanding picolinic acid degradation and its underlying molecular mechanism.
吡啶酸（PA）是一种典型的 C-2 羧酸化吡啶衍生物，是哺乳动物和微生物细胞中 l-色氨酸和许多其他芳香族化合物的代谢物。微生物可以降解和利用 PA 来生长。然而，PA 代谢的确切机制仍不清楚。
JQ135 菌株利用 PA 作为其碳氮源进行生长。在这项研究中，我们通过随机转座子诱变筛选出一种 6-羟基吡啶酸（6HPA）降解缺陷突变体。该突变体将 6HPA 羟化为中间产物，鉴定为 3,6-二羟基吡啶酸（3,6DHPA），不再进一步降解。一种新型脱羧酶 PicC 被鉴定为负责 3,6DHPA 的脱羧生成 2,5-二羟基吡啶。尽管 PicC 属于酰胺水解酶 2 家族，但与其他报道的酰胺水解酶 2 家族脱羧酶相比，其相似性（<45%）较低。此外，在使用 PicC 和相关蛋白构建的系统发育树中，发现 PicC 形成了一个单系群。此外，基因缺失和互补实验结果表明， 对于 PA 降解是必需的。 PicC 是一种依赖 Zn 的非氧化脱羧酶，可特异性催化 3,6DHPA 的不可逆脱羧生成 2,5-二羟基吡啶。对 3,6DHPA 的 和 分别为 13.44 μM 和 4.77 s。定点突变显示 His163 和 His216 对 PicC 活性至关重要。本研究从分子水平上为 PA 的微生物代谢提供了新的见解。
吡啶酸是一种源自 l-色氨酸代谢和哺乳动物及微生物细胞中其他芳香族化合物的天然毒性吡啶。微生物可以降解和利用吡啶酸来生长，因此已经提出了一种微生物降解吡啶酸的途径。吡啶酸依次转化为 6-羟基吡啶酸、3,6-二羟基吡啶酸和 2,5-二羟基吡啶。然而，该途径在生理和遗传上都没有得到验证。本研究表明 3,6-二羟基吡啶酸是吡啶酸分解代谢的中间产物，并进一步鉴定和表征了一种新型酰胺水解酶 2 家族脱羧酶 PicC。PicC 还被证明可以催化 3,6-二羟基吡啶酸的脱羧生成 2,5-二羟基吡啶。本研究为理解吡啶酸降解及其潜在分子机制提供了依据。
