Jiang Ruisheng, Kountz Duncan J, Zhang Liwen, Krzycki Joseph A
Department of Microbiology, The Ohio State University, Columbus, Ohio, USA.
Campus Chemical Instrument Center Mass Spectrometry and Proteomics Facility, The Ohio State University, Columbus, Ohio, USA.
J Biol Chem. 2025 Apr 23;301(6):108524. doi: 10.1016/j.jbc.2025.108524.
Elevated serum levels of trimethylamine N-oxide (TMAO) are reported to promote the development of atherosclerosis. TMAO is produced by hepatic oxidation of trimethylamine (TMA) produced by the gut microbiome from dietary quaternary amines such as choline. Net TMA production in the gut depends on microbial enzymes that either produce or consume TMA and its precursors. Here we report the elucidation of a novel microbial pathway consuming choline without TMA production. The human gut acetogen Eubacterium limosum grows by demethylating choline to N-N-dimethylaminoethanol. Quantitative mass spectral analysis of the proteome revealed a multi-protein choline to tetrahydrofolate (THF) methyltransferase system present only in choline-grown cells. The components are encoded in a gene cluster on the genome and include MthB, an MttB superfamily member; MthC, homologous to methylotrophic cobalamin-binding proteins; MthA, homologous to cobalamin:THF methyltransferases; and MthK, a protein related to serine kinases. Together, MthB, MthC, and MthA methylate THF with phosphocholine, but not choline or other quaternary amines. MthB specifically methylates Co(I)-MthC with phosphocholine. MthK acts as a bifunctional choline kinase which can utilize ATP or the MthB demethylation product, N,N-dimethylaminoethanol phosphate, to phosphorylate choline. Together, MthK, MthB, MthC, and MthA are proposed to carry out the methylation of THF with choline. These results outline a THF methylation pathway in which choline is first activated with ATP to phosphocholine prior to demethylation to form N,N-dimethylaminoethanol phosphate. The latter can be recycled by MthK to form more phosphocholine without expending additional ATP, thus minimizing energy utilization during choline-dependent acetogenesis.
据报道，血清中氧化三甲胺（TMAO）水平升高会促进动脉粥样硬化的发展。TMAO是由肠道微生物群从饮食中的季胺（如胆碱）产生的三甲胺（TMA）经肝脏氧化生成的。肠道中TMA的净生成取决于产生或消耗TMA及其前体的微生物酶。在此，我们报告了一条不产生TMA而消耗胆碱的新型微生物途径。人类肠道产乙酸菌迟缓真杆菌通过将胆碱去甲基化为N，N-二甲基氨基乙醇来生长。蛋白质组的定量质谱分析显示，仅在胆碱培养的细胞中存在一种多蛋白胆碱到四氢叶酸（THF）甲基转移酶系统。这些组分由基因组上的一个基因簇编码，包括MthB，一种MttB超家族成员；MthC，与甲基营养型钴胺素结合蛋白同源；MthA，与钴胺素：THF甲基转移酶同源；以及MthK，一种与丝氨酸激酶相关的蛋白质。MthB、MthC和MthA一起用磷酸胆碱而非胆碱或其他季胺对THF进行甲基化。MthB用磷酸胆碱特异性地使Co（I）-MthC甲基化。MthK作为一种双功能胆碱激酶，可利用ATP或MthB的去甲基化产物N，N-二甲基氨基乙醇磷酸将胆碱磷酸化。MthK、MthB、MthC和MthA一起被认为可利用胆碱对THF进行甲基化。这些结果概述了一条THF甲基化途径，其中胆碱首先用ATP激活为磷酸胆碱，然后去甲基化形成N，N-二甲基氨基乙醇磷酸。后者可被MthK循环利用以形成更多的磷酸胆碱，而无需消耗额外的ATP，从而在胆碱依赖性产乙酸过程中使能量利用最小化。
