Identification of the iroA Gene Product of Neisseria meningitidis as a Lactoferrin Receptor

The iroA gene product is an iron limitation-inducible outer membrane protein of Neisseria meningitidis. A spontaneous mutant lacking the gene was unable to bind lactoferrin. Furthermore, Escherichia coli strains expressing the IroA protein were capable of binding lactoferrin. Apparently, the IroA protein functions as a lactoferrin receptor. Efficient iron acquisition is an important virulence factor for many pathogens (2, 9). The concentration of free iron in the human host is low. Many bacteria cope with iron limitation by the synthesis and secretion of small iron chelators called siderophores (14). The iron-siderophore complexes are bound by specific receptors on the cell surface. Transport of the complexes across the outer membrane requires cytoplasmic membrane energy, which is, in Escherichia coli, coupled to the system via the TonB protein (17). Neisseria meningitidis and Neisseria gonorrhoeae do not produce siderophores. These bacteria are able to take up iron directly from transferrin i