Moraxella catarrhalis is a Gram-negative bacterium that is responsible for a substantial proportion of upper respiratory infections in children and lower respiratory infections in the elderly. Moraxella catarrhalis resides exclusively on the mucosal surfaces of the upper respiratory tract of humans and is capable of directly acquiring iron for growth from the host glycoproteins human transferrin (hTf) and human lactoferrin (hLf). The iron-bound form of these glycoproteins is initially captured by the surface lipoproteins Tf or Lf binding protein B (TbpB or LbpB) and delivered to the integral outer membrane TonB-dependent transport (TBDT) proteins, Tf binding protein A (TbpA) or Lf binding protein A (LbpA). The extraction of iron involves conformational changes in Lf and Tf to facilitate iron removal followed by its transport across the outer membrane by a well characterized process for TBDTs. Surprisingly the disruption of the gene encoding another TBDT, CopB, results in a reduction in the ability to grow on human Tf or Lf. The possibility that this could have been due to an artifact of mutant construction that resulted in the inhibition of TonB-mediated process was eliminated by a complete deletion of the CopB gene. A systematic evaluation of the impact on growth under various conditions by deletions of the genes encoding TbpA, LbpA, and CopB as well as mutations of the iron liganding residues and TonB box region of CopB was implemented. The results indicate that although CopB is capable of effectively acquiring iron from the growth medium, it does not directly acquire iron from Tf or Lf. We propose that the indirect effect on iron transport from Tf and Lf by CopB could possibly be explained by the association of TBDTs at gaps in the peptidoglycan layer that may enhance the efficiency of the process. This concept is supported by previous studies demonstrating an indirect effect on growth of Tf and Lf by deletion of the peptidoglycan binding outer membrane lipoprotein RmpM in Neisseria that also reduced the formation of larger complexes of TBDTs.

卡他莫拉菌 是一种革兰氏阴性细菌，儿童上呼吸道感染和老年人下呼吸道感染的很大一部分是由该细菌引起的。 卡他莫拉菌仅存在于人类上呼吸道的粘膜表面，能够从宿主糖蛋白人转铁蛋白 (hTf) 和人乳铁蛋白 (hLf) 中直接获取生长所需的铁。这些糖蛋白的铁结合形式最初被表面脂蛋白 Tf 或 Lf 结合蛋白 B（TbpB 或 LbpB）捕获并传递到完整的外膜 TonB 依赖性转运 (TBDT) 蛋白、Tf 结合蛋白 A (TbpA) 或Lf 结合蛋白 A (LbpA)。铁的提取涉及 Lf 和 Tf 的构象变化，以促进铁去除，然后通过对 TBDT 进行充分表征的过程将其运输穿过外膜。令人惊讶的是，编码另一种 TBDT CopB 的基因的破坏导致在人类 Tf 或 Lf 上生长的能力降低。这可能是由于突变体构建的人工产物导致 TonB 介导的过程受到抑制的可能性通过完全删除 CopB 基因而消除。通过删除编码 TbpA、LbpA 和 CopB 的基因以及 CopB 的铁配体残基和 TonB 盒区域的突变，对各种条件下对生长的影响进行了系统评估。结果表明，虽然 CopB 能够有效地从生长培养基中获取铁，但它不能直接从 Tf 或 Lf 中获取铁。我们提出，CopB 对来自 Tf 和 Lf 的铁转运的间接影响可能可以通过 TBDT 在肽聚糖层间隙处的关联来解释，这可能会提高该过程的效率。奈瑟菌属 这也减少了更大的 TBDT 复合物的形成。