title: Structural bases for heme binding and diatomic ligand recognition in truncated hemoglobins.
abstract: Truncated hemoglobins (trHbs) are low-molecular-weight oxygen-binding heme-proteins distributed in eubacteria, cyanobacteria, unicellular eukaryotes, and in higher plants, constituting a distinct group within the hemoglobin (Hb) superfamily. TrHbs display amino acid sequences 20-40 residues shorter than classical (non)vertebrate Hbs and myoglobins, to which they are scarcely related by sequence similarity. The trHb tertiary structure is based on a 2-on-2 alpha-helical sandwich, which represents a striking editing of the highly conserved 3-on-3 alpha-helical globin fold, achieved through deletion/truncation of alpha-helices and specific residue substitutions. Despite their 'minimal' polypeptide chain span, trHbs display an inner tunnel/cavity system held to support ligand diffusion to/from the heme distal pocket, accumulation of heme ligands within the protein matrix, and/or multiligand reactions. Moreover, trHbs bind and effectively stabilize the heme and recognize diatomic ligands (i.e., O2, CO, NO, and cyanide), albeit with varying thermodynamic and kinetic parameters. Here, structural bases for heme binding and diatomic ligand recognition by trHbs are reviewed.
authors.affiliation: Institute Giannina Gaslini, Largo Giannina Gaslini 5, 16147 Genova, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Milani
authors.forename: Alessandra
authors.initials: A
authors.lastname: Pesce
authors.forename: Marco
authors.initials: M
authors.lastname: Nardini
authors.forename: Hugues
authors.initials: H
authors.lastname: Ouellet
authors.forename: Yannick
authors.initials: Y
authors.lastname: Ouellet
authors.forename: Sylvia
authors.initials: S
authors.lastname: Dewilde
authors.forename: Alessio
authors.initials: A
authors.lastname: Bocedi
authors.forename: Paolo
authors.initials: P
authors.lastname: Ascenzi
authors.forename: Michel
authors.initials: M
authors.lastname: Guertin
authors.forename: Luc
authors.initials: L
authors.lastname: Moens
authors.forename: Joel M
authors.initials: JM
authors.lastname: Friedman
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Wittenberg
authors.forename: Martino
authors.initials: M
authors.lastname: Bolognesi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002248:Carbon Monoxide / Q000737:chemistry; D003486:Cyanides / Q000737:chemistry; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009569:Nitric Oxide / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D011487:Protein Conformation; D016415:Sequence Alignment; D054793:Truncated Hemoglobins
chemical_list: D003486:Cyanides; D006454:Hemoglobins; D008024:Ligands; D054793:Truncated Hemoglobins; D009569:Nitric Oxide; D006418:Heme; D002248:Carbon Monoxide; D010100:Oxygen