期刊
JOURNAL OF INORGANIC BIOCHEMISTRY
卷 99, 期 1, 页码 97-109出版社
ELSEVIER SCIENCE INC
DOI: 10.1016/j.jinorgbio.2004.10.035
关键词
truncated hemoglobin; hemoglobin; myoglobin; heme stabilization; diatomic ligand recognition; protein cavities
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., O-2, 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. (C) 2004 Elsevier Inc. All rights reserved.
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