Identification of an outer-membrane haemoglobin-binding protein in Neisseria meningitidis.
Although Neisseria meningitidis can use haemoglobin as an iron source in vitro, the mechanism of haemoglobin-iron uptake is unknown. Using a biotinylated human haemoglobin probe in a solid-phase dot-binding assay, haemoglobin-binding activity was detected in total membranes derived from meningococci grown under iron-limited but not iron-sufficient conditions. In competition binding experiments, bovine and human haemoglobin could abrogate binding. In contrast, no binding inhibition was seen with ferric nitrate, protoporphyrin IX, and iron-loaded human transferrin. The ability of both haemin and catalase, a nonhaemoglobin haem-containing compound, to inhibit binding competitively suggested that the ligand recognized by the binding protein is the haem moiety. Scatchard plot analysis revealed a heterogeneous receptor population. Limited proteolysis with proteinase K abolished binding activity, suggesting a haemoglobin-protein interaction. Detection of activity in a whole-cell binding assay demonstrated that this haemin-binding protein was surface exposed. In a limited survey of meningococcal strains, the presence of haemoglobin-binding activity in all isolates indicated that expression of this binding protein is not serogroup specific.
Lee
B C
BC
Department of Microbiology and Infectious Diseases, University of Calgary, Canada.
Hill
P
P
D001425:Bacterial Outer Membrane Proteins / Q000032:analysis / Q000302:isolation & purification* / Q000378:metabolism; D001426:Bacterial Proteins; D001692:Biological Transport; D001710:Biotin; D002352:Carrier Proteins / Q000032:analysis / Q000302:isolation & purification* / Q000378:metabolism; D019286:Endopeptidase K; D014644:Genetic Variation; D006454:Hemoglobins / Q000378:metabolism*; D007501:Iron / Q000378:metabolism* / Q000494:pharmacology; D015335:Molecular Probes; D009345:Neisseria meningitidis / Q000254:growth & development / Q000378:metabolism*; D011990:Receptors, Transferrin / Q000096:biosynthesis; D012697:Serine Endopeptidases / Q000494:pharmacology; D013347:Subcellular Fractions / Q000737:chemistry
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D006454:Hemoglobins; D015335:Molecular Probes; D011990:Receptors, Transferrin; C017206:hemoglobin-binding protein, bacteria; D001710:Biotin; D007501:Iron; D012697:Serine Endopeptidases; D019286:Endopeptidase K