Phosphocholine molecules decorating bacterial cell wall teichoic acids and outer-membrane lipopolysaccharide have significant roles in adhesion to host cells, immune evasion, and persistence. Bacteria carrying the operon that performs phosphocholine decoration, synthesize phosphocholine after uptake of the choline precursor by LicB, a conserved transporter among divergent species. Streptococcus pneumoniae is a prominent pathogen where phosphocholine decoration plays a fundamental role in virulence. Here we present cryo-electron microscopy and crystal structures of S. pneumoniae LicB, revealing distinct conformational states and describing architectural and mechanistic elements essential to choline import. Together with in vitro and in vivo functional characterization, we found that LicB displays proton-coupled import activity and promiscuous selectivity involved in adaptation to choline deprivation conditions, and describe LicB inhibition by synthetic nanobodies (sybodies) and hemicholinium-3. Our results provide novel insights into the molecular mechanism of a key transporter involved in bacterial pathogenesis and establish a basis for inhibition of the phosphocholine modification pathway across bacterial phyla.

中文翻译：

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磷壁酸和脂多糖修饰中胆碱输入的机制基础

装饰细菌细胞壁磷壁酸和外膜脂多糖的磷胆碱分子在与宿主细胞的粘附、免疫逃避和持久性方面具有重要作用。携带进行磷酸胆碱修饰的操纵子的细菌在被 LicB 摄取胆碱前体后合成磷酸胆碱，LicB 是不同物种之间的保守转运蛋白。肺炎链球菌是一种突出的病原体，其中磷酸胆碱修饰在毒力中起着重要作用。在这里，我们展示了肺炎链球菌LicB 的低温电子显微镜和晶体结构，揭示了不同的构象状态并描述了对胆碱输入至关重要的结构和机械元素。连同体外和体内在功能表征方面，我们发现 LicB 显示出质子耦合输入活性和参与对胆碱剥夺条件的适应的混杂选择性，并描述了合成纳米抗体（sybodies）和半胆碱 3 对 LicB 的抑制作用。我们的研究结果提供了对参与细菌发病机制的关键转运蛋白的分子机制的新见解，并为抑制跨细菌门的磷酸胆碱修饰途径奠定了基础。