1d8u | pdb_00001d8u
CRYSTAL STRUCTURE OF NON-SYMBIOTIC PLANT HEMOGLOBIN FROM RICE
Structural highlights
FunctionNSHB1_ORYSJ Phytoglobin that reduces nitrite to nitric oxide under anoxic conditions (e.g. during flooding or in waterlogged soil) (PubMed:21495624). May not function as an oxygen storage or transport protein (PubMed:17540516, PubMed:9390447). Has an unusually high affinity for O(2) through a hexacoordinate heme iron because of a very low dissociation constant (PubMed:9390447).[1] [2] [3] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedBACKGROUND: 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. 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[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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