1d8u
From Proteopedia
|
CRYSTAL STRUCTURE OF NON-SYMBIOTIC PLANT HEMOGLOBIN FROM RICE
Overview
BACKGROUND: Nonsymbiotic hemoglobins (nsHbs) form a new class of plant, proteins that is distinct genetically and structurally from, leghemoglobins. They are found ubiquitously in plants and are expressed in, low concentrations in a variety of tissues including roots and leaves., Their function involves a biochemical response to growth under limited, O(2) conditions. RESULTS: The first X-ray crystal structure of a member of, this class of proteins, riceHb1, has been determined to 2.4 A resolution, using a combination of phasing techniques. The active site of ferric, riceHb1 differs significantly from those of traditional hemoglobins and, myoglobins. The proximal and distal histidine sidechains coordinate, directly to the heme iron, forming a hemichrome with spectral properties, similar to those of cytochrome b(5). The crystal structure also shows that, riceHb1 is a dimer with a novel interface formed by close contacts between, the G helix and the region between the B and C helices of the partner, subunit. CONCLUSIONS: The bis-histidyl heme coordination found in riceHb1, is unusual for a protein that binds O(2) reversibly. However, the distal, His73 is rapidly displaced by ferrous ligands, and the overall O(2), affinity is ultra-high (K(D) approximately 1 nM). Our crystallographic, model suggests that ligand binding occurs by an upward and outward, movement of the E helix, concomitant dissociation of the distal histidine, possible repacking of the CD corner and folding of the D helix. Although, the functional relevance of quaternary structure in nsHbs is unclear, the, role of two conserved residues in stabilizing the dimer interface has been, identified.
About this Structure
1D8U is a Single protein structure of sequence from Oryza sativa with HEM as ligand. Full crystallographic information is available from OCA.
Reference
Crystal structure of a nonsymbiotic plant hemoglobin., Hargrove MS, Brucker EA, Stec B, Sarath G, Arredondo-Peter R, Klucas RV, Olson JS, Phillips GN Jr, Structure. 2000 Sep 15;8(9):1005-14. PMID:10986467
Page seeded by OCA on Thu Nov 8 12:59:46 2007
