Bacterial surface polysaccharides are assembled by glycosyltransferase enzymes that typically use sugar nucleotide or polyprenyl-monophosphosugar activated donors. Characterized representatives exist for many monosaccharides but neither the donor nor the corresponding glycosyltransferases have been definitively identified for ribofuranose residues found in some polysaccharides. Klebsiella pneumoniae O-antigen polysaccharides provided prototypes to identify dual-domain ribofuranosyltransferase proteins catalyzing a two-step reaction sequence. Phosphoribosyl-5-phospho-d-ribosyl-α-1-diphosphate serves as the donor for a glycan acceptor-specific phosphoribosyl transferase (gPRT), and a more promiscuous phosphoribosyl-phosphatase (PRP) then removes the residual 5′-phosphate. The 2.5-Å resolution crystal structure of a dual-domain ribofuranosyltransferase ortholog from Thermobacillus composti revealed a PRP domain that conserves many features of the phosphatase members of the haloacid dehalogenase family, and a gPRT domain that diverges substantially from all previously characterized phosphoribosyl transferases. The gPRT represents a new glycosyltransferase fold conserved in the most abundant ribofuranosyltransferase family.

细菌表面多糖由糖基转移酶组装而成，这些酶通常使用糖核苷酸或聚异戊二烯基单磷酸糖激活的供体。许多单糖存在特征代表，但对于某些多糖中发现的呋喃核糖残基，供体和相应的糖基转移酶均未明确鉴定。肺炎克雷伯菌O 抗原多糖提供了用于识别催化两步反应序列的双域呋喃核糖基转移酶蛋白的原型。Phosphoribosyl-5-phospho- d-核糖基-α-1-二磷酸作为聚糖受体特异性磷酸核糖基转移酶（gPRT）的供体，然后更混杂的磷酸核糖基磷酸酶（PRP）去除残留的5'-磷酸。来自复合嗜热杆菌的双结构域呋喃核糖基转移酶直向同源物的 2.5 Å 分辨率晶体结构揭示了一个 PRP 结构域，该结构域保留了卤酸脱卤酶家族的磷酸酶成员的许多特征，以及一个与所有先前表征的磷酸核糖基转移酶大不相同的 gPRT 结构域。gPRT 代表了在最丰富的呋喃核糖基转移酶家族中保守的新糖基转移酶折叠。