Campylobacter jejuni is a Gram-negative pathogenic bacterium commonly found in chickens and is the leading cause of human diarrheal disease worldwide. The various serotypes of C. jejuni produce structurally distinct capsular polysaccharides (CPSs) on the exterior surfaces of the cell wall. The capsular polysaccharide from C. jejuni serotype HS:5 is composed of a repeating sequence of d-glycero-d-manno-heptose and d-glucitol-6-phosphate. We previously defined the pathway for the production of d-glycero-d-manno-heptose in C. jejuni. Here, we elucidate the biosynthetic pathway for the assembly of cytidine diphosphate (CDP)-6-d-glucitol by the combined action of two previously uncharacterized enzymes. The first enzyme catalyzes the formation of CDP-6-d-fructose from cytidine triphosphate (CTP) and d-fructose-6-phosphate. The second enzyme reduces CDP-6-d-fructose with NADPH to generate CDP-6-d-glucitol. Using sequence similarity network (SSN) and genome neighborhood network (GNN) analyses, we predict that these pairs of proteins are responsible for the biosynthesis of CDP-6-d-glucitol and/or CDP-d-mannitol in the lipopolysaccharides (LPSs) and capsular polysaccharides in more than 200 other organisms. In addition, high resolution X-ray structures of the second enzyme are reported, which provide novel insight into the manner in which an open-chain nucleotide-linked sugar is harbored in an active site cleft.

中文翻译：

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空肠弯曲杆菌荚膜多糖胞苷二磷酸-6-d-葡萄糖醇的生物合成

空肠弯曲菌是一种革兰氏阴性致病菌，常见于鸡中，是全世界人类腹泻病的主要原因。空肠弯曲菌的各种血清型在细胞壁的外表面产生结构不同的荚膜多糖（CPS）。来自空肠弯曲菌血清型 HS:5的荚膜多糖由d-甘油-d-甘露-庚糖和d-葡萄糖醇-6-磷酸重复序列组成。我们之前定义了空肠弯曲菌中生产d-甘油-d-甘露-庚糖的途径。在这里，我们阐明了通过两种先前未表征的酶的联合作用组装胞苷二磷酸（CDP）-6- d-葡萄糖醇的生物合成途径。第一种酶催化胞苷三磷酸（CTP）和d-果糖-6-磷酸形成 CDP-6- d-果糖。第二种酶用NADPH还原CDP-6- d-果糖以生成CDP-6- d-葡萄糖醇。使用序列相似性网络（SSN）和基因组邻域网络（GNN）分析，我们预测这些蛋白质对负责脂多糖（LPS）中CDP-6 -d-葡萄糖醇和/或CDP- d-甘露醇的生物合成以及 200 多种其他生物体中的荚膜多糖。此外，还报道了第二种酶的高分辨率X射线结构，这为了解开链核苷酸连接的糖在活性位点裂缝中的藏匿方式提供了新的见解。