title: Characterization of the hgbA locus encoding a hemoglobin receptor from Haemophilus ducreyi.
abstract: Haemophilus ducreyi can bind hemoglobin and use it as a source of heme, for which it has an obligate requirement. We previously identified and purified HgbA, a hemoglobin-binding outer membrane protein from H. ducreyi. In this report, we describe the molecular cloning, expression, DNA sequence, and mutagenesis of the structural gene for HgbA, hgbA. H. ducreyi and recombinant Escherichia coli expressing hgbA bound [125I]hemoglobin, establishing HgbA as a receptor. Insertions or deletions in the cloned hgbA gene abolished expression of HgbA and hemoglobin binding in E. coli. Mutagenesis of H. ducreyi by allelic exchange of insertions into hgbA abolished its ability to bind [125I]hemoglobin or utilize hemoglobin as a source of heme. The deduced protein sequence was similar to those of the TonB-dependent family of outer membrane receptors. The most similar member was HutA (heme receptor) from Vibrio cholerae. Tbp1 and Lbp1 (transferrin and lactoferrin receptors, respectively, from pathogenic Neisseria spp.) also showed very significant homology. Thus, by characterizing the hgbA locus, this work elucidates a potentially important role of HgbA in obtaining heme and/or iron from the host.
authors.affiliation: Department of Medicine, School of Medicine, University of North Carolina, Chapel Hill 27599, USA.
authors.forename: C
authors.initials: C
authors.lastname: Elkins
authors.forename: C J
authors.initials: CJ
authors.lastname: Chen
authors.forename: C E
authors.initials: CE
authors.lastname: Thomas
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D006191:Haemophilus ducreyi / Q000235:genetics*; D006454:Hemoglobins / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D017386:Sequence Homology, Amino Acid
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D006454:Hemoglobins; D008565:Membrane Proteins; C017206:hemoglobin-binding protein, bacteria; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli