title: The first structure from the SOUL/HBP family of heme-binding proteins, murine P22HBP.
abstract: Murine p22HBP, a 22-kDa monomer originally identified as a cytosolic heme-binding protein ubiquitously expressed in various tissues, has 27% sequence identity to murine SOUL, a heme-binding hexamer specifically expressed in the retina. In contrast to murine SOUL, which binds one heme per subunit via coordination of the Fe(III)-heme to a histidine, murine p22HBP binds one heme molecule per subunit with no specific axial ligand coordination of the Fe(III)-heme. Using intrinsic protein fluorescence quenching, the values for the dissociation constants of p22HBP for hemin and protoporphyrin-IX were determined to be in the low nanomolar range. The three-dimensional structure of murine p22HBP, the first for a protein from the SOUL/HBP family, was determined by NMR methods to consist of a 9-stranded distorted beta-barrel flanked by two long alpha-helices. Although homologous domains have been found in three bacterial proteins, two of which are transcription factors, the fold determined for p22HBP corresponds to a novel alpha plus beta fold in a eukaryotic protein. Chemical shift mapping localized the tetrapyrrole binding site to a hydrophobic cleft formed by residues from helix alphaA and an extended loop. In an attempt to assess the structural basis for tetrapyrrole binding in the SOUL/HBP family, models for the p22HBP-protoporphyrin-IX complex and the SOUL protein were generated by manual docking and automated methods.
authors.affiliation: Rede de Química e Tecnologia, Centro de Química Fina e Biotecnologia, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: Jorge S
authors.initials: JS
authors.lastname: Dias
authors.forename: Anjos L
authors.initials: AL
authors.lastname: Macedo
authors.forename: Gloria C
authors.initials: GC
authors.lastname: Ferreira
authors.forename: Francis C
authors.initials: FC
authors.lastname: Peterson
authors.forename: Brian F
authors.initials: BF
authors.lastname: Volkman
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Goodfellow
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry / Q000502:physiology*; D006418:Heme / Q000737:chemistry*; D000081062:Heme-Binding Proteins; D006420:Hemeproteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D006427:Hemin / Q000737:chemistry; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D011524:Protoporphyrins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D045725:Tetrapyrroles / Q000737:chemistry
chemical_list: D002352:Carrier Proteins; C000631029:HEBP1 protein, human; C469231:Hebp1 protein, mouse; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D011524:Protoporphyrins; D045725:Tetrapyrroles; D006418:Heme; D006427:Hemin; C028025:protoporphyrin IX