title: The extracellular heme-binding protein HbpS from the soil bacterium Streptomyces reticuli is an aquo-cobalamin binder.
abstract: The extracellular protein HbpS from Streptomyces reticuli interacts with iron ions and heme. It also acts in concert with the two-component sensing system SenS-SenR in response to oxidative stress. Sequence comparisons suggested that the protein may bind a cobalamin. UV-visible spectroscopy confirmed binding (Kd = 34 μm) to aquo-cobalamin (H2OCbl(+)) but not to other cobalamins. Competition experiments with the H2OCbl(+)-coordinating ligand CN(-) and comparison of mutants identified a histidine residue (His-156) that coordinates the cobalt ion of H2OCbl(+) and substitutes for water. HbpS·Cobalamin lacks the Asp-X-His-X-X-Gly motif seen in some cobalamin binding enzymes. Preliminary tests showed that a related HbpS protein from a different species also binds H2OCbl(+). Furthermore, analyses of HbpS-heme binding kinetics are consistent with the role of HbpS as a heme-sensor and suggested a role in heme transport. Given the high occurrence of HbpS-like sequences among Gram-positive and Gram-negative bacteria, our findings suggest a great functional versatility among these proteins.
authors.affiliation: From the Applied Genetics of Microorganisms, Department of Biology/Chemistry, University of Osnabrueck, 49067 Osnabrueck, Germany, ortiz@biologie.uni-osnabrueck.de.
authors.forename: Darío
authors.initials: D
authors.lastname: Ortiz de Orué Lucana
authors.affiliation: Department of Engineering, Aarhus University, 8000 Aarhus, Denmark, and.
authors.forename: Sergey N
authors.initials: SN
authors.lastname: Fedosov
authors.affiliation: From the Applied Genetics of Microorganisms, Department of Biology/Chemistry, University of Osnabrueck, 49067 Osnabrueck, Germany.
authors.forename: Ina
authors.initials: I
authors.lastname: Wedderhoff
authors.affiliation: From the Applied Genetics of Microorganisms, Department of Biology/Chemistry, University of Osnabrueck, 49067 Osnabrueck, Germany.
authors.forename: Edith N
authors.initials: EN
authors.lastname: Che
authors.affiliation: Centre for Bioinformatics, Hamburg University, 20146 Hamburg, Germany.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Torda
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D015870:Gene Expression; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D000081062:Heme-Binding Proteins; D006420:Hemeproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D012988:Soil Microbiology; D013302:Streptomyces / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D040681:Structural Homology, Protein; D014805:Vitamin B 12 / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D011994:Recombinant Proteins; C043960:aquacobalamin; D006418:Heme; D006639:Histidine; D007501:Iron; D014805:Vitamin B 12
keywords: Bioinformatics; Ligand-binding Protein; Metalloprotein; Microbiology; Spectroscopy