1.B.14.2.4
Lactoferrin receptor (A=OMR porin; B=lipoprotein), LbpAB or IroAB. This two-component system extracts iron from the host glycoproteins lactoferrin and transferrin. Homologous iron-transport systems consist of a membrane-bound transporter and an accessory lipoprotein. The crystal structure of the N-terminal domain (N-lobe) of the accessory lipoprotein, lactoferrin-binding protein B (LbpB) is homologous to the structures of the accessory lipoproteins, transferrin-binding protein B (TbpB) and LbpB from the bovine pathogen Moraxella bovis. Docking the LbpB  with lactoferrin reveals extensive binding interactions with the N1 subdomain of lactoferrin. The nature of the interaction precludes apolactoferrin from binding LbpB, ensuring the specificity for iron-loaded lactoferrin, safeguarding proper delivery of iron-bound lactoferrin to the transporter LbpA. The structure also reveals a possible secondary role for LbpB in protecting the bacteria from host defences. Following proteolytic digestion of lactoferrin, a cationic peptide derived from the N-terminus is released. This peptide, called lactoferricin, exhibits potent antimicrobial effects. The docked model of LbpB with lactoferrin reveals that LbpB interacts extensively with the N-terminal lactoferricin region (Brooks et al. 2014).