Neutrophil gelatinase-associated lipocalin expresses antimicrobial activity by interfering with L-norepinephrine-mediated bacterial iron acquisition.
l-norepinephrine (NE) is a neuroendocrine catecholamine that supports bacterial growth by mobilizing iron from a primary source such as holotransferrin to increase its bioavailability for cellular uptake. Iron complexes of NE resemble those of bacterial siderophores that are scavenged by human neutrophil gelatinase-associated lipocalin (NGAL) as part of the innate immune defense. Here, we show that NGAL binds iron-complexed NE, indicating physiological relevance for both bacterial and human iron metabolism. The fluorescence titration of purified recombinant NGAL with the Fe(III).(NE)(3) iron complex revealed high affinity for this ligand, with a K(D) of 50.6 nM. In contrast, the binding protein FeuA of Bacillus subtilis, which is involved in the bacterial uptake of triscatecholate iron complexes, has a K(D) for Fe(III).(NE)(3) of 1.6 muM, indicating that NGAL is an efficient competitor. Furthermore, NGAL was shown to inhibit the NE-mediated growth of both E. coli and B. subtilis strains that either are capable or incapable of producing their native siderophores enterobactin and bacillibactin, respectively. These experiments suggest that iron-complexed NE directly serves as an iron source for bacterial uptake systems, and that NGAL can function as an antagonist of this iron acquisition process. Interestingly, a functional FeuABC uptake system was shown to be necessary for NE-mediated growth stimulation as well as its NGAL-dependent inhibition. This study demonstrates for the first time that human NGAL not only neutralizes pathogen-derived virulence factors but also can effectively scavenge an iron-chelate complex abundant in the host.
Miethke
Marcus
M
Munich Center for Integrated Protein Science, CIPS-M, Lehrstuhl für Biologische Chemie, Technische Universität München, 85350 Freising-Weihenstephan, Germany.
Skerra
Arne
A
D000209:Acute-Phase Proteins / Q000235:genetics / Q000378:metabolism*; D000900:Anti-Bacterial Agents / Q000378:metabolism*; D001412:Bacillus subtilis / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D004837:Epinephrine / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D008024:Ligands; D000071068:Lipocalin-2; D054834:Lipocalins / Q000235:genetics / Q000378:metabolism*; D009638:Norepinephrine / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017262:Siderophores / Q000378:metabolism
D000209:Acute-Phase Proteins; D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins; C489506:LCN2 protein, human; D008024:Ligands; D000071068:Lipocalin-2; D054834:Lipocalins; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; D017262:Siderophores; C028593:colicin receptor, E coli; D007501:Iron; D009638:Norepinephrine; D004837:Epinephrine