Errickson Simons Max, Narindoshvili Tamari, Raushel Frank M
Department of Biochemistry & Biophysics, Texas A&M University, College Station, Texas 77842, United States.
Department of Chemistry, Texas A&M University, College Station, Texas 77842, United States.
Biochemistry. 2025 Aug 19;64(16):3623-3633. doi: 10.1021/acs.biochem.5c00296. Epub 2025 Aug 8.
is a Gram-negative human pathogen and is the most common cause of gastroenteritis in the United States and Europe. expresses a capsular polysaccharide (CPS) that enables the evasion of the host immune response and adherence to host epithelial cells. The various subspecies (serotypes) of are distinguished by their unique CPS repeating units. The repeating trisaccharide in the HS:41 serotype was previously found to contain l-arabinofuranose, 6-deoxy-d--heptofuranose, and a third sugar, which is either d-fucofuranose or 6-deoxy-l-altrofuranose. Genome neighborhood and sequence similarity networks were employed to identify five candidate genes for the biosynthesis of d-fucofuranose and 6-deoxy-l-altrofuranose. Here, it was demonstrated that the biosynthetic pathways for both sugars are initiated by the formation of CDP-d-glucose from CTP and d-glucose-1-phosphate as catalyzed by HS41.21. This product is dehydrated by an NAD-dependent 4,6-dehydratase (HS41.20) that produces CDP-4-keto-6-deoxy-d-glucose. The third enzyme (HS41.19) was shown to catalyze the inversion of stereochemistry at C3 and C5 using CDP-4-keto-6-deoxy-d-glucose as the substrate. The fourth enzyme (HS41.18) is an NADPH-dependent C4-reductase that catalyzes the formation of CDP-d-fucopyranose from CDP-4-keto-6-deoxy-d-glucose in the absence of the 3,5-epimerase but catalyzes the formation of CDP-6-deoxy-l-altropyranose in the presence of the epimerase. The last enzyme (HS41.17) in the pathway was shown to catalyze the FADH-dependent interconversion of CDP-d-fucopyranose and CDP-6-deoxy-l-altropyranose to CDP-d-fucofuranose and CDP-6-deoxy-l-altrofuranose, respectively. The overall synthesis of the two possible products is governed by the catalytic activity of the epimerase, since the C4-reductase and pyranose-furanose mutase are not affected by the stereochemistry at C5.
是一种革兰氏阴性人类病原体，是美国和欧洲肠胃炎最常见的病因。它表达一种荚膜多糖（CPS），这种多糖能够逃避宿主免疫反应并黏附于宿主上皮细胞。的各种亚种（血清型）通过其独特的CPS重复单元来区分。先前发现HS:41血清型中的重复三糖含有L-阿拉伯呋喃糖、6-脱氧-D-甘露庚呋喃糖以及第三种糖，该糖要么是D-岩藻呋喃糖，要么是6-脱氧-L-阿卓呋喃糖。利用基因组邻域和序列相似性网络来鉴定D-岩藻呋喃糖和6-脱氧-L-阿卓呋喃糖生物合成的五个候选基因。在此，证明了这两种糖的生物合成途径均由HS41.21催化CTP和D-葡萄糖-1-磷酸形成CDP-D-葡萄糖起始。该产物由一种依赖NAD的4,6-脱水酶（HS41.20）脱水，生成CDP-4-酮-6-脱氧-D-葡萄糖。第三种酶（HS41.19）被证明以CDP-4-酮-6-脱氧-D-葡萄糖为底物催化C3和C5处立体化学的反转。第四种酶（HS41.18）是一种依赖NADPH的C4-还原酶，在没有3,5-表异构酶的情况下，它催化由CDP-4-酮-6-脱氧-D-葡萄糖形成CDP-D-岩藻吡喃糖，但在有表异构酶存在时，它催化形成CDP-6-脱氧-L-阿卓吡喃糖。该途径中的最后一种酶（HS41.17）被证明分别催化依赖FADH的CDP-D-岩藻吡喃糖和CDP-6-脱氧-L-阿卓吡喃糖相互转化为CDP-D-岩藻呋喃糖和CDP-6-脱氧-L-阿卓呋喃糖。两种可能产物的整体合成受表异构酶催化活性的控制，因为C4-还原酶和吡喃糖-呋喃糖变位酶不受C5处立体化学的影响。
