Abstract：
The major nutrients available to the human colonic microbiota are complex glycans derived from the diet. To degrade this highly variable mix of sugar structures, gut microbes have acquired a huge array of different carbohydrate-active enzymes (CAZymes), predominantly glycoside hydrolases, many of which have specificities that can be exploited for a range of different applications. Plant N-glycans are prevalent on proteins produced by plants and thus components of the diet, but the breakdown of these complex molecules by the gut microbiota has not been explored. Plant N-glycans are also well characterized allergens in pollen and some plant-based foods, and when plants are used in heterologous protein production for medical applications, the N-glycans present can pose a risk to therapeutic function and stability. Here we use a novel genome association approach for enzyme discovery to identify a breakdown pathway for plant complex N-glycans encoded by a gut Bacteroides species and biochemically characterize five CAZymes involved, including structures of the PNGase and GH92 α-mannosidase. These enzymes provide a toolbox for the modification of plant N-glycans for a range of potential applications. Furthermore, the keystone PNGase also has activity against insect-type N-glycans, which we discuss from the perspective of insects as a nutrient source.
摘要：
人类结肠微生物群可用的主要营养素是源自饮食的复合聚糖。为了降解这种高度可变的糖结构混合物，肠道微生物已经获得了大量不同的碳水化合物活性酶（CAZymes），主要是糖苷水解酶，其中许多具有可用于一系列不同应用的特异性。植物N-聚糖普遍存在于植物产生的蛋白质上，因此也是饮食的组成部分，但是这些复杂分子被肠道微生物群分解的过程还没有被探索。植物N-聚糖也是花粉和一些植物性食物中具有良好特征的过敏原，当植物被用于医学应用的异源蛋白质生产时，存在的N-聚糖可对治疗功能和稳定性构成风险。在这里，我们使用一种新的基因组关联方法来发现酶，以鉴定由肠道拟杆菌属物种编码的植物复杂N-聚糖的分解途径，并在生物化学上表征所涉及的五个CAZyme，包括PNGase和GH92α-甘露糖苷酶的结构。这些酶为植物N-聚糖的修饰提供了一个工具箱，用于一系列潜在的应用。此外，keystonePNGase还具有抗昆虫型N-聚糖的活性，我们从昆虫作为营养来源的角度来讨论。
