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首页> 外文期刊>Infection and immunity >Identification of Discrete Domains within Gonococcal Transferrin-Binding Protein A That Are Necessary for Ligand Binding and Iron Uptake Functions
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Identification of Discrete Domains within Gonococcal Transferrin-Binding Protein A That Are Necessary for Ligand Binding and Iron Uptake Functions

机译：淋球菌转铁蛋白结合蛋白A内的离散域的识别，这是配体结合和铁摄取功能所必需的

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The availability of free iron in vivo is strictly limited, in part by the iron-binding protein transferrin. The pathogenicNeisseria spp. can sequester iron from this protein, dependent upon two iron-repressible, transferrin-binding proteins (TbpA and TbpB). TbpA is a TonB-dependent, integral, outer membrane protein that may form a β-barrel exposing multiple surface loops, some of which are likely to contain ligand-binding motifs. In this study we propose a topological model of gonococcal TbpA and then test some of the hypotheses set forth by the model by individually deleting three putative loops (designated loops 4, 5, and 8). Each mutant TbpA could be expressed without toxicity and was surface exposed as assessed by immunoblotting, transferrin binding, and protease accessibility. Deletion of loop 4 or loop 5 abolished transferrin binding to whole cells in solid- and liquid-phase assays, while deletion of loop 8 decreased the affinity of the receptor for transferrin without affecting the copy number. Strains expressing any of the three mutated TbpAs were incapable of growth on transferrin as a sole iron source. These data implicate putative loops 4 and 5 as critical determinants for receptor function and transferrin-iron uptake by gonococcal TbpA. The phenotype of the ΔL8TbpA mutant suggests that high-affinity ligand interaction is required for transferrin-iron internalization.
机译：体内游离铁的可用性受到严格限制，部分受铁结合蛋白运铁蛋白的限制。致病性奈瑟菌属。可以从铁蛋白中螯合铁，这取决于两个可抑制铁的转铁蛋白结合蛋白（TbpA和TbpB）。 TbpA是依赖TonB的完整外膜蛋白，可形成暴露于多个表面环的β-桶，其中一些环可能含有配体结合基序。在这项研究中，我们提出了淋球菌TbpA的拓扑模型，然后通过分别删除三个假定的环（指定的环4、5和8）来检验该模型提出的某些假设。通过免疫印迹，转铁蛋白结合和蛋白酶可及性评估，每种突变体TbpA均可表达而无毒性，且表面暴露。在固相和液相测定中，环4或环5的缺失消除了转铁蛋白与全细胞的结合，而环8的缺失降低了受体对转铁蛋白的亲和力而不影响拷贝数。表达这三个突变的TbpA中任何一个的菌株都不能在转铁蛋白上作为唯一的铁源生长。这些数据暗示推定的环4和5是淋球菌TbpA受体功能和转铁蛋白铁摄取的关键决定因素。 ΔL8TbpA突变体的表型表明，转铁蛋白-铁内在化需要高亲和力的配体相互作用。

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