1rps
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Crystallographic Analysis of the Interaction of Nitric Oxide with Quaternary-T Human Hemoglobin. Hemoglobin exposed to NO under anerobic conditions
OverviewOverview
In addition to interacting with hemoglobin as a heme ligand to form, nitrosylhemoglobin, NO can react with cysteine sulfhydryl groups to form, S-nitrosocysteine or cysteine oxides such as cysteinesulfenic acid. Both, modes of interaction are very sensitive to the quaternary structure of, hemoglobin. To directly view the interaction of NO with quaternary-T, deoxyhemoglobin, crystallographic studies were carried out on crystals of, deoxyhemoglobin that were exposed to gaseous NO under a variety of, conditions. Consistent with previous spectroscopic studies in solution, these crystallographic studies show that the binding of NO to the heme, groups of crystalline wild-type deoxyhemoglobin ruptures the Fe-proximal, histidine bonds of the alpha-subunits but not the beta-subunits. This, finding supports Perutz's theory that ligand binding induces tension in, the alpha Fe-proximal histidine bond. To test Perutz's theory, deoxy, crystals of the mutant hemoglobin betaW37E were exposed to NO. This, experiment was carried out because previous studies have shown that this, mutation greatly reduces the quaternary constraints that oppose the, ligand-induced movement of the alpha-heme Fe atom into the plane of the, porphyrin ring. As hypothesized, the Fe-proximal histidine bonds in both, the beta- and the alpha-subunits remain intact in crystalline betaW37E, after exposure to NO. With regard to S-nitrosocysteine or cysteine oxide, formation, no evidence for the reaction of NO with any cysteine residues, was detected under anaerobic conditions. However, when deoxyhemoglobin, crystals are first exposed to air and then to NO, the appearance of, additional electron density indicates that Cys93(F9)beta has been, modified, most likely to cysteinesulfenic acid. This modification of, Cys93(F9)beta disrupts the intrasubunit salt bridge between, His146(HC3)beta and Asp94(FG1)beta, a key feature of the quaternary-T, hemoglobin structure. Also presented is a reanalysis of our previous, crystallographic studies [Chan, N.-L., et al. (1998) Biochemistry 37, 16459-16464] of the interaction of NO with liganded hemoglobin in the, quaternary-R2 structure. These studies showed additional electron density, at Cys93(F9)beta that was consistent with an NO adduct. However, for, reasons discussed in this paper, we now believe that this adduct may be, the Hb-S-N.-O-H radical intermediate and not Hb-S-N=O as previously, suggested.
About this StructureAbout this Structure
1RPS is a Protein complex structure of sequences from Homo sapiens with HEM and NO as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Crystallographic analysis of the interaction of nitric oxide with quaternary-T human hemoglobin., Chan NL, Kavanaugh JS, Rogers PH, Arnone A, Biochemistry. 2004 Jan 13;43(1):118-32. PMID:14705937
Page seeded by OCA on Thu Nov 8 13:16:53 2007