State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, Guangxi, China.
Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom.
J Biol Chem. 2020 Dec 25;295(52):18625-18637. doi: 10.1074/jbc.RA120.014974. Epub 2020 Oct 23.
Pectins are a major dietary nutrient source for the human gut microbiota. The prominent gut microbe was recently shown to encode the founding member (BT1017) of a new family of pectin methylesterases essential for the metabolism of the complex pectin rhamnogalacturonan-II (RG-II). However, biochemical and structural knowledge of this family is lacking. Here, we showed that BT1017 is critical for the metabolism of an RG-II-derived oligosaccharide ΔBT1017oligoB generated by a BT1017 deletion mutant (ΔBT1017) during growth on carbohydrate extract from apple juice. Structural analyses of ΔBT1017oligoB using a combination of enzymatic, mass spectrometric, and NMR approaches revealed that it is a bimethylated nonaoligosaccharide (GlcA-β1,4-(2--Me-Xyl-α1,3)-Fuc-α1,4-(GalA-β1,3)-Rha-α1,3-Api-β1,2-(Ara-α1,3)-(GalA-α1,4)-GalA) containing components of the RG-II backbone and its side chains. We showed that the catalytic module of BT1017 adopts an α/β-hydrolase fold, consisting of a central twisted 10-stranded β-sheet sandwiched by several α-helices. This constitutes a new fold for pectin methylesterases, which are predominantly right-handed β-helical proteins. Bioinformatic analyses revealed that the family is dominated by sequences from prominent genera of the human gut microbiota, including and Our re-sults not only highlight the critical role played by this family of enzymes in pectin metabolism but also provide new insights into the molecular basis of the adaptation of to the human gut.
果胶是人类肠道微生物群的主要膳食营养来源。最近发现，突出的肠道微生物 编码了果胶甲酯酶新家族的创始成员（BT1017），该酶对于复杂果胶鼠李半乳糖醛酸聚糖-II（RG-II）的代谢至关重要。然而，该家族的生化和结构知识仍然缺乏。在这里，我们表明，BT1017 对于代谢由 BT1017 缺失突变体（ΔBT1017）在生长过程中产生的源自 RG-II 的寡糖 ΔBT1017oligoB 至关重要，该寡糖是由来自苹果汁碳水化合物提取物的 BT1017 缺失产生的。使用酶、质谱和 NMR 方法的组合对 ΔBT1017oligoB 进行结构分析表明，它是一种双甲基化的九糖（GlcA-β1,4-(2--Me-Xyl-α1,3)-Fuc-α1,4-(GalA-β1,3)-Rha-α1,3-Api-β1,2-(Ara-α1,3)-(GalA-α1,4)-GalA），含有 RG-II 主链及其侧链的成分。我们表明，BT1017 的催化模块采用 α/β-水解酶折叠，由一个中心扭曲的 10 股β-折叠夹在几个α-螺旋之间。这构成了果胶甲酯酶的一个新折叠，果胶甲酯酶主要是右手β-螺旋蛋白。生物信息学分析表明，该家族主要由人类肠道微生物群中突出属的序列主导，包括 和 。我们的结果不仅突出了该酶家族在果胶代谢中所起的关键作用，而且为 适应人类肠道的分子基础提供了新的见解。
