Nicotinamide N-methyltransferase (NNMT) is one of the most abundant small molecule methyltransferases in the human body and is primarily responsible for the N-methylation of the nicotinamide (vitamin B3). Employing the cofactor S-adenosyl-l-methionine, NNMT transfers a methyl group to the pyridine nitrogen of nicotinamide to generate N-methylnicotinamide. Interestingly, NNMT is also able to N-methylate a variety of other pyridine-containing small molecules, suggesting a secondary role for the enzyme in the detoxification of xenobiotics. A number of recent studies have also revealed links between NNMT overexpression and a variety of diseases, including multiple cancers, Parkinson’s disease, diabetes, and obesity. To facilitate further study of both the substrate scope and potential for inhibitor development, we here describe the development of a new NNMT activity assay. The assay makes use of ultra-high-performance hydrophilic interaction chromatography, allowing for rapid separation of the reaction products, coupled with quadrupole time-of-flight mass spectrometric detection, providing for enhanced sensitivity and enabling high-throughput sample analysis. We successfully demonstrated the general applicability of the method by performing kinetic analyses of NNMT-mediated methylation for a range of pyridine-based substrates. These findings also provide new insight into the diversity of substrate recognition by NNMT in a quantitative manner. In addition, we further established the suitability of the assay for the identification and characterization of small molecule inhibitors of NNMT. To do so, we investigated the inhibition of NNMT by the nonspecific methyltransferase inhibitors sinefungin and S-adenosyl-l-homocysteine, revealing IC50 values in the low micromolar range. The results of these inhibition studies are particularly noteworthy as they will permit future efforts toward the development of new NNMT-specific inhibitors.
烟酰胺 N-甲基转移酶(NN
MT)是人体内含量最多的小分子甲基转移酶之一,主要负责烟酰胺(
维生素 B3)的 N-甲基化。利用辅助因子 S-
腺苷-l-蛋
氨酸,NN
MT 将一个甲基转移到烟酰胺的
吡啶氮上,生成 N-甲基烟酰胺。有趣的是,NN
MT 还能对其他多种含
吡啶的小分子进行 N 甲基化,这表明该酶在解毒异种
生物方面起着辅助作用。最近的一些研究还揭示了 NN
MT 过度表达与多种疾病(包括多种癌症、帕
金森病、糖尿病和肥胖症)之间的联系。为了促进对底物范围和
抑制剂开发潜力的进一步研究,我们在此介绍一种新型 NN
MT 活性测定法的开发情况。该测定利用超高效亲
水相互作用色谱法快速分离反应产物,并结合四极杆飞行时间质谱检测,提高了灵敏度,实现了高通量样品分析。通过对一系列基于
吡啶的底物进行 NN
MT 介导的甲基化动力学分析,我们成功证明了该方法的普遍适用性。这些发现也为定量了解 NN
MT 识别底物的多样性提供了新的视角。此外,我们还进一步确定了该检测方法在鉴定和表征 NN
MT 小分子
抑制剂方面的适用性。为此,我们研究了非特异性甲基转移酶
抑制剂松香菌素和 S-
腺苷-l-高半胱
氨酸对 NN
MT 的抑制作用,结果显示 IC50 值在较低的微摩尔范围内。这些抑制研究的结果特别值得注意,因为它们将有助于今后开发新的 NN
MT 特异性
抑制剂。