The lactoferrin receptor complex in Gram negative bacteria

Abstract

Bacteria that inhabit the respiratory and genitourinary tracts of mammals encounter an iron-deficient environment on the mucosal surface where iron is complexed by the host iron-binding proteins transferrin and lactoferrin. Lactoferrin is also present in high concentrations at sites of inflammation where the cationic anti-microbial peptide lactoferricin is produced by proteolysis of lactoferrin. Several members of the Neisseriaceae and Moraxellaceae families express surface receptors, capable of specifically binding host lactoferrin and extracting the iron from lactoferrin as a source of iron for growth. The receptor is comprised of an integral outer membrane protein, lactoferrin binding protein A (LbpA), and a largely exposed surface lipoprotein, lactoferrin binding protein B (LbpB). LbpA is essential for mediating growth using lactoferrin as a sole iron source whereas LbpB only plays a facilitating role. LbpB, with the presence of a large tract of negatively charged residues, appears to protect the bacterial cell from the bactericidal effects of the lactoferricin. The lactoferrin receptors in these species appear to be essential for survival and thus may serve as potential vaccine targets.