Lipopolysaccharide O-antigen is an attractive candidate for immunotherapeutic strategies targeting antibiotic-resistant Klebsiella pneumoniae. Several K. pneumoniae O-serotypes are based on a shared O2a-antigen backbone repeating unit: (→ 3)-α-Galp-(1 → 3)-β-Galf-(1 →). O2a antigen is synthesized on undecaprenol diphosphate in a pathway involving the O2a polymerase, WbbM, before its export by an ATP-binding cassette transporter. This dual domain polymerase possesses a C-terminal galactopyranosyltransferase resembling known GT8 family enzymes, and an N-terminal DUF4422 domain identified here as a galactofuranosyltransferase defining a previously unrecognized family (GT111). Functional assignment of DUF4422 explains how galactofuranose is incorporated into various polysaccharides of importance in vaccine production and the food industry. In the 2.1-Å resolution structure, three WbbM protomers associate to form a flattened triangular prism connected to a central stalk that orients the active sites toward the membrane. The biochemical, structural and topological properties of WbbM offer broader insight into the mechanisms of assembly of bacterial cell-surface glycans.

脂多糖O抗原是针对抗生素耐药性肺炎克雷伯菌的免疫治疗策略的有吸引力的候选物。几个肺炎克雷伯菌O型血清型是基于共享O2A抗原骨架的重复单元：（→3）-α-Gal的p - （1→3）-β-Gal的˚F-（1→）。O2a抗原是通过十一碳烯醇二磷酸在涉及O2a聚合酶WbbM的途径中合成的，然后由ATP结合盒转运蛋白输出。该双结构域聚合酶具有类似于已知GT8家族酶的C端半乳糖吡喃糖基转移酶，以及一个N端DUF4422结构域，在此被识别为定义了先前未被认识的家族的半乳糖呋喃糖基转移酶（GT111）。DUF4422的功能分配说明了半乳糖呋喃糖如何掺入疫苗生产和食品工业中重要的各种多糖中。在2.1-Å分辨率的结构中，三个WbbM前驱子结合在一起，形成一个扁平的三角棱镜，该棱镜与中央茎相连，该茎将活性部位朝向膜定向。生化