Institute of Nutritional Sciences, Nutrigenomics Section, Friedrich Schiller University Jena, Jena, Germany.
Institute for Inorganic and Analytical Chemistry, Friedrich Schiller University Jena, Jena, Germany.
Redox Biol. 2021 Jul;43:101972. doi: 10.1016/j.redox.2021.101972. Epub 2021 Apr 15.
Methanethiol, a gas with the characteristic smell of rotten cabbage, is a product of microbial methionine degradation. In the human body, methanethiol originates primarily from bacteria residing in the lumen of the large intestine. Selenium-binding protein 1 (SELENBP1), a marker protein of mature enterocytes, has recently been identified as a methanethiol oxidase (MTO). It catalyzes the conversion of methanethiol to hydrogen sulfide (HS), hydrogen peroxide (HO) and formaldehyde. Here, human Caco-2 intestinal epithelial cells were subjected to enterocyte-like differentiation, followed by analysis of SELENBP1 levels and MTO activity. To that end, we established a novel coupled assay to assess MTO activity mimicking the proximity of microbiome and intestinal epithelial cells in vivo. The assay is based on in situ-generation of methanethiol as catalyzed by a bacterial recombinant l-methionine gamma-lyase (MGL), followed by detection of HS and HO. Applying this assay, we verified the loss and impairment of MTO function in SELENBP1 variants (His329Tyr; Gly225Trp) previously identified in individuals with familial extraoral halitosis. MTO activity was strongly enhanced in Caco-2 cells upon enterocyte differentiation, in parallel with increased SELENBP1 levels. This suggests that mature enterocytes located at the tip of colonic crypts are capable of eliminating microbiome-derived methanethiol.
甲硫醇是一种具有腐烂白菜气味的气体，是微生物蛋氨酸降解的产物。在人体中，甲硫醇主要来源于大肠腔中的细菌。硒结合蛋白 1（SELENBP1）是成熟肠细胞的标志物蛋白，最近被鉴定为甲硫醇氧化酶（MTO）。它催化甲硫醇转化为硫化氢（HS）、过氧化氢（HO）和甲醛。在这里，我们使人类 Caco-2 肠上皮细胞进行肠细胞样分化，然后分析 SELENBP1 水平和 MTO 活性。为此，我们建立了一种新的偶联测定法来评估 MTO 活性，模拟微生物组和体内肠上皮细胞的接近度。该测定法基于细菌重组 l-蛋氨酸 γ-裂合酶（MGL）催化原位生成甲硫醇，然后检测 HS 和 HO。应用该测定法，我们验证了先前在家族性口腔异味个体中发现的 SELENBP1 变体（His329Tyr；Gly225Trp）中 MTO 功能的丧失和损伤。在 Caco-2 细胞进行肠细胞分化时，MTO 活性强烈增强，同时 SELENBP1 水平升高。这表明位于结肠隐窝顶端的成熟肠细胞能够消除微生物组衍生的甲硫醇。
