Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, USA.
mBio. 2012 Jul 10;3(4). doi: 10.1128/mBio.00158-12. Print 2012.
Coenzyme A (CoA) is essential for cellular chemistry in all forms of life. The pantothenate moiety of CoA is generated from the condensation of pantoate and β-alanine. β-Alanine is formed by decarboxylation of l-aspartate catalyzed by PanD, a pyruvoyl enzyme that is synthesized by the cell as an inactive precursor (pro-PanD). Maturation of pro-PanD into PanD occurs via a self-cleavage event at residue Ser25, which forms the catalytic pyruvoyl moiety. We recently reported that Salmonella enterica PanM was necessary for pro-PanD maturation, both in vitro and in vivo. Notably, PanM is annotated as a Gcn5-like N-acetyltransferase (GNAT), which suggested that lysine acetylation might be part of the mechanism of maturation. Here we show that PanM lacks acetyltransferase activity and that acetyl-CoA stimulates its activity. Results of experiments with nonhydrolyzable ethyl-CoA and genetically encoded acetyl-lysine-containing PanD support the conclusion that PanM-dependent pro-PanD maturation does not involve an acetyl transfer event. We also show that CoA binding to PanM is needed for in vivo activity and that disruption of CoA binding prevents PanM from interacting with PanD. We conclude that PanM is a GNAT homologue that lost its acetyltransferase activity and evolved a new function as an acetyl-CoA sensor that can trigger the maturation of pro-PanD.
Nε-lysine acetylation is increasingly being recognized as a widespread and important form of posttranslational regulation in bacteria. The acetyltransferases that catalyze these reactions are poorly characterized in bacteria. Based on annotation, most bacterial genomes contain several acetyltransferases, but the physiological roles of only a handful have been determined. Notably, a subset of putative acetyltransferases lack residues that are critical for activity in most biochemically characterized acetyltransferases. We show that one such putative acetyltransferase, PanM (formerly YhhK), lacks acetyltransferase activity but functions instead as an acetyl-coenzyme A (CoA) sensor. This work establishes the possibility that, like PanM, other putative acetyltransferases may have evolved new functions while retaining the ability to sense acetyl-CoA.
辅酶 A（CoA）是所有生命形式细胞化学的必需物质。CoA 的泛酸盐部分是由泛酸和β-丙氨酸缩合生成的。β-丙氨酸是由天冬氨酸经 PanD 催化脱羧形成的，PanD 是一种由细胞合成的无活性前体（pro-PanD）的丙酮酸酶。pro-PanD 成熟为 PanD 是通过残基 Ser25 的自我切割事件发生的，该事件形成了催化性的丙酮酸部分。我们最近报道称，沙门氏菌 PanM 是 pro-PanD 成熟所必需的，无论是在体外还是体内。值得注意的是，PanM 被注释为 Gcn5 样 N-乙酰转移酶（GNAT），这表明赖氨酸乙酰化可能是成熟机制的一部分。在这里，我们表明 PanM 缺乏乙酰转移酶活性，并且乙酰辅酶 A 会刺激其活性。使用不可水解的乙基-CoA 和遗传编码的含乙酰-赖氨酸的 PanD 进行实验的结果支持这样的结论，即 PanM 依赖性 pro-PanD 成熟不涉及乙酰转移事件。我们还表明，CoA 与 PanM 的结合对于体内活性是必需的，并且 CoA 结合的破坏阻止了 PanM 与 PanD 的相互作用。我们得出结论，PanM 是一个失去乙酰转移酶活性并演变为新功能的 GNAT 同源物，作为乙酰辅酶 A 的传感器，可以触发 pro-PanD 的成熟。
Nε-赖氨酸乙酰化作为一种广泛存在且重要的细菌翻译后调控形式，正逐渐被认识到。催化这些反应的乙酰转移酶在细菌中特征描述较差。根据注释，大多数细菌基因组包含几种乙酰转移酶，但只有少数几种的生理作用已经确定。值得注意的是，一组假定的乙酰转移酶缺乏大多数生物化学特征乙酰转移酶中对活性至关重要的残基。我们表明，这样一种假定的乙酰转移酶 PanM（以前称为 YhhK）缺乏乙酰转移酶活性，但作为乙酰辅酶 A（CoA）传感器发挥作用。这项工作确立了这样一种可能性，即像 PanM 一样，其他假定的乙酰转移酶可能在保留感知乙酰-CoA 的能力的同时，已经进化出了新的功能。
