Structural insight into the dual function of LbpB in mediating Neisserial pathogenesis
Lactoferrin binding protein B (LbpB) is a lipoprotein present on the surface of Neisseria that has been postulated to serve dual functions during pathogenesis in both iron acquisition from lactoferrin, and in providing protection against the cationic antimicrobial peptide lactoferricin. Here, we present the structures of LbpB from N. meningitidis and N. gonorrhoeae in complex with human holo-lactoferrin, forming a 1:1 complex and confirmed by SEC-SAXS. LbpB consists of N- and C-lobes with the N-lobe interacting extensively with the C-lobe of lactoferrin. Our structures provides insight into LbpBs preference towards holo-lactoferrin, and our mutagenesis and binding studies show that lactoferrin and lactoferricin bind independently. Our studies provide the molecular details for how LbpB serves to capture and preserve lactoferrin in an iron-bound state for delivery to the membrane transporter LbpA for iron piracy, and as an antimicrobial peptide sink to evade host immune defenses.