Ostan Nicholas K H, Yu Rong-Hua, Ng Dixon, Lai Christine Chieh-Lin, Pogoutse Anastassia K, Sarpe Vladimir, Hepburn Morgan, Sheff Joey, Raval Shaunak, Schriemer David C, Moraes Trevor F, Schryvers Anthony B
Department of Microbiology & Infectious Diseases, University of Calgary, Calgary, Alberta, Canada.
Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada.
PLoS Pathog. 2017 Mar 3;13(3):e1006244. doi: 10.1371/journal.ppat.1006244. eCollection 2017 Mar.
Lactoferrin binding protein B (LbpB) is a bi-lobed outer membrane-bound lipoprotein that comprises part of the lactoferrin (Lf) receptor complex in Neisseria meningitidis and other Gram-negative pathogens. Recent studies have demonstrated that LbpB plays a role in protecting the bacteria from cationic antimicrobial peptides due to large regions rich in anionic residues in the C-terminal lobe. Relative to its homolog, transferrin-binding protein B (TbpB), there currently is little evidence for its role in iron acquisition and relatively little structural and biophysical information on its interaction with Lf. In this study, a combination of crosslinking and deuterium exchange coupled to mass spectrometry, information-driven computational docking, bio-layer interferometry, and site-directed mutagenesis was used to probe LbpB:hLf complexes. The formation of a 1:1 complex of iron-loaded Lf and LbpB involves an interaction between the Lf C-lobe and LbpB N-lobe, comparable to TbpB, consistent with a potential role in iron acquisition. The Lf N-lobe is also capable of binding to negatively charged regions of the LbpB C-lobe and possibly other sites such that a variety of higher order complexes are formed. Our results are consistent with LbpB serving dual roles focused primarily on iron acquisition when exposed to limited levels of iron-loaded Lf on the mucosal surface and effectively binding apo Lf when exposed to high levels at sites of inflammation.
乳铁蛋白结合蛋白B(LbpB)是一种双叶的外膜结合脂蛋白,它是脑膜炎奈瑟菌和其他革兰氏阴性病原体中乳铁蛋白(Lf)受体复合物的一部分。最近的研究表明,由于C端叶中富含阴离子残基的大片区域,LbpB在保护细菌免受阳离子抗菌肽的侵害中发挥作用。相对于其同源物转铁蛋白结合蛋白B(TbpB),目前几乎没有证据表明它在铁摄取中的作用,并且关于其与Lf相互作用的结构和生物物理信息也相对较少。在本研究中,结合交联和氘交换并耦合质谱、信息驱动的计算对接、生物层干涉测量和定点诱变来探测LbpB:hLf复合物。载铁Lf与LbpB形成1:1复合物涉及Lf C叶与LbpB N叶之间的相互作用,这与TbpB类似,与铁摄取中的潜在作用一致。Lf N叶也能够与LbpB C叶的带负电荷区域以及可能的其他位点结合,从而形成多种高阶复合物。我们的结果与LbpB发挥双重作用一致,当在粘膜表面暴露于有限水平的载铁Lf时,主要专注于铁摄取,而在炎症部位暴露于高水平时则有效结合脱铁Lf。