Structural bases for heme binding and diatomic ligand recognition in truncated hemoglobins.
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.
Milani
Mario
M
Institute Giannina Gaslini, Largo Giannina Gaslini 5, 16147 Genova, Italy.
Pesce
Alessandra
A
Nardini
Marco
M
Ouellet
Hugues
H
Ouellet
Yannick
Y
Dewilde
Sylvia
S
Bocedi
Alessio
A
Ascenzi
Paolo
P
Guertin
Michel
M
Moens
Luc
L
Friedman
Joel M
JM
Wittenberg
Jonathan B
JB
Bolognesi
Martino
M
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
D003486:Cyanides; D006454:Hemoglobins; D008024:Ligands; D054793:Truncated Hemoglobins; D009569:Nitric Oxide; D006418:Heme; D002248:Carbon Monoxide; D010100:Oxygen