Key Laboratory of Systematic Mycology and Lichenology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.
Biochem Biophys Res Commun. 2011 Jul 1;410(2):212-7. doi: 10.1016/j.bbrc.2011.05.092. Epub 2011 May 23.
Several bacteria causing meningitis, such as Escherichia coli K1, Streptococcus suis, Neisseria meningitidis, and group B Streptococci (GBS), produce sialic acid (Neu5Ac)-containing capsular polysaccharide (CPS). Biosynthesis of the Neu5Ac-containing CPS requires CMP-Neu5Ac as substrate, which is synthesized by CMP-Neu5Ac synthetase from CTP and Neu5Ac. In E. coli or GBS, the NeuA protein encoded by the neuA gene has been known encoding a bifunctional enzyme that possesses both CMP-Neu5Ac synthetase and O-acetylesterase activity. In this report, we found that the S. suis NeuA (SsNeuA) was also a bifunctional CMP-Neu5Ac synthetase/O-acetylesterase. Biochemical analyses revealed that the SsNeuA strictly de-O-acetylated CMP-O-acetyl-Neu5Ac, whereas the E. coli NeuA (EcNeuA) preferentially de-O-acetylated CMP-O-acetyl-Neu5Ac. E. coli devoid of NeuA O-acetylesterase activity was unable to produce capsule and only CMP-Neu5Ac synthetase activity of the EcNeuA or SsNeuA could not restore its ability to produce capsule. These results suggest that the O-acetylesterase is essential for the synthesis of capsular Neu5Ac in E. coli, probably in S. suis and GBS as well. Our findings are key to understanding the biosynthesis of capsular Neu5Ac in E. coli, S. suis and GBS.
几种引起脑膜炎的细菌，如大肠杆菌 K1、猪链球菌、脑膜炎奈瑟菌和 B 群链球菌（GBS），会产生含有唾液酸（Neu5Ac）的荚膜多糖（CPS）。Neu5Ac 含有 CPS 的生物合成需要 CMP-Neu5Ac 作为底物，而 CMP-Neu5Ac 则由 CTP 和 Neu5Ac 通过 CMP-Neu5Ac 合成酶合成。在大肠杆菌或 GBS 中，neuA 基因编码的 NeuA 蛋白已被证实编码一种具有 CMP-Neu5Ac 合成酶和 O-乙酰基酯酶活性的双功能酶。在本报告中，我们发现猪链球菌 NeuA（SsNeuA）也是一种双功能的 CMP-Neu5Ac 合成酶/O-乙酰基酯酶。生化分析表明，SsNeuA 严格地去乙酰化 CMP-O-乙酰-Neu5Ac，而大肠杆菌 NeuA（EcNeuA）则优先去乙酰化 CMP-O-乙酰-Neu5Ac。缺乏 NeuA O-乙酰基酯酶活性的大肠杆菌无法产生荚膜，只有 EcNeuA 或 SsNeuA 的 CMP-Neu5Ac 合成酶活性无法恢复其产生荚膜的能力。这些结果表明，O-乙酰基酯酶对于大肠杆菌中荚膜 Neu5Ac 的合成是必不可少的，在猪链球菌和 GBS 中也可能如此。我们的发现对于理解大肠杆菌、猪链球菌和 GBS 中荚膜 Neu5Ac 的生物合成具有关键意义。
