Kelly Steven D, Williams Danielle M, Nothof Jeremy T, Kim Taeok, Lowary Todd L, Kimber Matthew S, Whitfield Chris
Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada.
Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada.
Nat Chem Biol. 2022 May;18(5):530-537. doi: 10.1038/s41589-022-01006-6. Epub 2022 Apr 7.
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多萜基单磷酸糖作为活化供体。许多单糖都有其特征性代表，但对于某些多糖中发现的呋喃核糖残基，其供体和相应的糖基转移酶尚未得到明确鉴定。肺炎克雷伯菌O抗原多糖为鉴定催化两步反应序列的双结构域呋喃核糖基转移酶蛋白提供了原型。5-磷酸核糖基-5-磷酸-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，然后一种更具通用性的磷酸核糖基磷酸酶（PRP）去除残留的5'-磷酸。来自嗜热芽孢杆菌的双结构域呋喃核糖基转移酶直系同源物的2.5埃分辨率晶体结构显示，PRP结构域保留了卤代酸脱卤酶家族磷酸酶成员的许多特征，而gPRT结构域与所有先前鉴定的磷酸核糖基转移酶有很大差异。gPRT代表了在最丰富的呋喃核糖基转移酶家族中保守的一种新的糖基转移酶折叠形式。
