Department of Biochemistry and Molecular Biology, University of Calgary, Canada.
Biochem J. 2012 Jun 1;444(2):189-97. doi: 10.1042/BJ20112133.
The ability to acquire iron directly from host Tf (transferrin) is an adaptation common to important bacterial pathogens belonging to the Pasteurellaceae, Moraxellaceae and Neisseriaceae families. A surface receptor comprising an integral outer membrane protein, TbpA (Tf-binding protein A), and a surface-exposed lipoprotein, TbpB (Tf-binding protein B), mediates the iron acquisition process. TbpB is thought to extend from the cell surface for capture of Tf to initiate the process and deliver Tf to TbpA. TbpA functions as a gated channel for the passage of iron into the periplasm. In the present study we have mapped the effect of TbpA from Actinobacillus pleuropneumoniae on pTf (porcine Tf) using H/DX-MS (hydrogen/deuterium exchange coupled to MS) and compare it with a previously determined binding site for TbpB. The proposed TbpA footprint is adjacent to and potentially overlapping the TbpB-binding site, and induces a structural instability in the TbpB site. This suggests that simultaneous binding to pTf by both receptors would be hindered. We demonstrate that a recombinant TbpB lacking a portion of its anchor peptide is unable to form a stable ternary TbpA-pTf-TbpB complex. This truncated TbpB does not bind to a preformed Tf-TbpA complex, and TbpA removes pTf from a preformed Tf-TbpB complex. Thus the results of the present study support a model whereby TbpB 'hands-off' pTf to TbpA, which completes the iron removal and transport process.
从宿主 Tf（转铁蛋白）中直接获取铁的能力是一种适应，常见于属于巴斯德氏菌科、莫拉氏菌科和奈瑟氏菌科的重要细菌病原体。一种由整合外膜蛋白 TbpA（转铁蛋白结合蛋白 A）和表面暴露的脂蛋白 TbpB（转铁蛋白结合蛋白 B）组成的表面受体，介导铁获取过程。TbpB 被认为从细胞表面延伸出来，用于捕获 Tf 以启动该过程并将 Tf 递送至 TbpA。TbpA 作为铁进入周质的门控通道发挥作用。在本研究中，我们使用 H/DX-MS（氢/氘交换与 MS 结合）研究了胸膜肺炎放线杆菌的 TbpA 对 pTf（猪转铁蛋白）的影响，并将其与先前确定的 TbpB 结合位点进行了比较。提出的 TbpA 足迹与 TbpB 结合位点相邻且可能重叠，并在 TbpB 位点引起结构不稳定。这表明两个受体同时结合 pTf 将受到阻碍。我们证明，缺乏一部分锚定肽的重组 TbpB 无法形成稳定的三元 TbpA-pTf-TbpB 复合物。这种截断的 TbpB 不能与预先形成的 Tf-TbpA 复合物结合，并且 TbpA 从预先形成的 Tf-TbpB 复合物中去除 pTf。因此，本研究的结果支持了一种模型，即 TbpB 将 pTf“交”给 TbpA，后者完成铁的去除和转运过程。
