Fig 5. Proposed functions of LbpB.

(LEFT) LbpB may be involved in the iron-acquisition pathway. At low concentrations of holo-hLf, LbpB may use its LbpB-N binding mode to preferentially bind iron-loaded lactoferrin and shuttle it to LbpA, forming a ternary complex and hijacking the iron. (RIGHT) Cleavage of LbpB from the membrane may be dependent on the presence of high levels of hLf in the extracellular milieu or simply a constitutive property of N. meningitidis cells in the NalP phase-variable ON-state. The release of LbpB from the membrane is done in an effort to sequester lactoferricin, antibodies, and possibly form large lattices of hLf as to prevent proteolytical processing into its derivative cationic antimicrobial peptides.