Structural highlights
Function[NP4_RHOPR] Heme-based protein that deliver nitric oxide gas (NO) to the victim while feeding, resulting in vasodilation and inhibition of platelet aggregation. Also bind tightly to histamine, which is released by the host to induce wound healing (By similarity). Publication Abstract from PubMedHeme proteins are important entities for the metabolism of nitrite. Inspection of the structural features of the reported hemoproteinnitrite crystal structures reveals that, except for nitrophorin 4 (NP4), H-bonding to the nitrite ligand is accomplished via histidine or arginine residues. These H-bonds probably play an important role for the nitrite coordination and/or reactivities. In nitrophorins, which catalyze the nitrite disproportionation reaction, such a residue is missing. Here, we report on the L130R mutant of the NP isoprotein NP4 that provides the Arg130 residue as part of the flexible GH loop as a potential H-bonding residue in the distal heme pocket. Similar to the wild-type protein, nitrite remains N-bonded in the crystal structure of NP4(L130R). However, spectroscopic investigations show that, in solution, a second ligand-rotational orientation exists, which is in fast-exchange equilibrium with the normal, parallel ligand orientation. Moreover, the nitrite disproportionation is inhibited in NP4(L130R). Comparison with another, also less active mutant NP4(D30N) suggests that the displacement of H(2) O molecules from the heme cavity prevents the proton donation pathway through Asp30. Insertion of an h-bonding residue into the distal pocket of the ferriheme protein nitrophorin 4: effect on nitriteiron coordination and nitrite disproportionation.,He C, Ogata H, Knipp M Chem Biodivers. 2012 Sep;9(9):1761-75. doi: 10.1002/cbdv.201100401. PMID:22976968[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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