title: A gene cluster involved in the utilization of both free heme and heme:hemopexin by Haemophilus influenzae type b.
abstract: The utilization of heme bound to the serum glycoprotein hemopexin by Haemophilus influenzae type b (Hib) strain DL42 requires the presence of the 100-kDa heme:hemopexin-binding protein encoded by the hxuA gene (M. S. Hanson, S. E. Pelzel, J. Latimer, U. Muller-Eberhard, and E. J. Hansen, Proc. Natl. Acad. Sci. USA 89:1973-1977, 1992). Nucleotide sequence analysis of a 5-kb region immediately upstream from the hxuA gene revealed the presence of two genes, designated hxuC and hxuB, which encoded outer membrane proteins. The 78-kDa HxuC protein had similarity to TonB-dependent outer membrane proteins of other organisms, whereas the 60-kDa HxuB molecule most closely resembled the ShlB protein of Serratia marcescens. A set of three isogenic Hib mutants with cat cartridges inserted individually into their hxuA, hxuB, and hxuC genes was constructed. None of these mutants could utilize heme:hemopexin. The hxuC mutant was also unable to utilize low levels of free heme, whereas both the hxuA and hxuB mutants could utilize free heme. When the wild-type hxuC gene was present in trans, the hxuC mutant regained its ability to utilize low levels of free heme but still could not utilize heme:hemopexin. The hxuA mutant could utilize heme:hemopexin when a functional hxuA gene from a nontypeable H. influenzae strain was present in trans. Complementation analysis using this cloned nontypeable H. influenzae hxuA gene also indicated that the HxuB protein likely functions in the release of soluble HxuA from the Hib cell. These studies indicate that at least two and possible three gene products are required for utilization of heme bound to hemopexin by Hib strain DL42.
authors.affiliation: Department of Microbiology, University of Texas Southwestern Medical Center, Dallas 75235, USA.
authors.forename: L D
authors.initials: LD
authors.lastname: Cope
authors.forename: R
authors.initials: R
authors.lastname: Yogev
authors.forename: U
authors.initials: U
authors.lastname: Muller-Eberhard
authors.forename: E J
authors.initials: EJ
authors.lastname: Hansen
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D001692:Biological Transport; D005798:Genes, Bacterial / Q000235:genetics*; D006193:Haemophilus influenzae / Q000235:genetics* / Q000378:metabolism; D006418:Heme / Q000378:metabolism*; D006466:Hemopexin / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D016254:Mutagenesis, Insertional; D016366:Open Reading Frames / Q000235:genetics; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D015183:Restriction Mapping; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; C028027:heme receptor; C057616:tonB protein, Bacteria; C489182:tonB protein, Haemophilus influenzae; D006418:Heme; D006466:Hemopexin