Solution NMR characterization of magnetic/electronic properties of azide and cyanide-inhibited substrate complexes of human heme oxygenase: Implications for steric ligand tilt
| Autor: | Gerd N. La Mar, Paul R. Ortiz de Montellano, Hiroshi Ogura, Dungeng Peng, Li-Hua Ma, John P. Evans |
|---|---|
| Rok vydání: | 2013 |
| Předmět: |
Azides
Stereochemistry Cyanide Electrons Heme Ligands Biochemistry Protein Structure Secondary Inorganic Chemistry chemistry.chemical_compound Catalytic Domain Humans Nuclear Magnetic Resonance Biomolecular Cyanides Molecular Structure biology Ligand Hydrogen bond Chemical shift Water Active site Hydrogen Bonding chemistry Heme Oxygenase (Decyclizing) Proton NMR biology.protein Anisotropy Thermodynamics Azide Protons Two-dimensional nuclear magnetic resonance spectroscopy |
| Zdroj: | Journal of Inorganic Biochemistry. 121:179-186 |
| ISSN: | 0162-0134 |
| DOI: | 10.1016/j.jinorgbio.2013.01.004 |
| Popis: | Solution 2D (1)H NMR was carried out on the azide-ligated substrate complex of human heme oxygenase, hHO, to provide information on the active site molecular structure, chromophore electronic/magnetic properties, and the distal H-bond network linked to the exogenous ligand by catalytically relevant oriented water molecules. While 2D NMR exhibited very similar patterns of two-dimensional nuclear Overhauser spectroscopy cross peaks of residues with substrate and among residues as the previously characterized cyanide complex, significant, broadly distributed chemical shift differences were observed for both labile and non-labile protons. The anisotropy and orientation of the paramagnetic susceptibility tensor, χ, were determined for both the azide and cyanide complexes. The most significant difference observed is the tilt of the major magnetic axes from the heme normal, which is only half as large for the azide than cyanide ligand, with each ligand tilted toward the catalytically cleaved α-meso position. The difference in chemical shifts is quantitatively correlated with differences in dipolar shifts in the respective complexes for all but the distal helix. The necessity of considering dipolar shifts, and hence determination of the orientation/anisotropy of χ, in comparing chemical shifts involving paramagnetic complexes, is emphasized. The analysis shows that the H-bond network cannot detect significant differences in H-bond acceptor properties of cyanide versus azide ligands. Lastly, significant retardation of distal helix labile proton exchange upon replacing cyanide with azide indicates that the dynamic stability of the distal helix is increased upon decreasing the steric interaction of the ligand with the distal helix. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|
Full Text from ScienceDirect