title: 1H NMR study of the effect of variable ligand on heme oxygenase electronic and molecular structure.
abstract: Heme oxygenase carries out stereospecific catabolism of protohemin to yield iron, CO and biliverdin. Instability of the physiological oxy complex has necessitated the use of model ligands, of which cyanide and azide are amenable to solution NMR characterization. Since cyanide and azide are contrasting models for bound oxygen, it is of interest to characterize differences in their molecular and/or electronic structures. We report on detailed 2D NMR comparison of the azide and cyanide substrate complexes of heme oxygenase from Neisseria meningitidis, which reveals significant and widespread differences in chemical shifts between the two complexes. To differentiate molecular from electronic structural changes between the two complexes, the anisotropy and orientation of the paramagnetic susceptibility tensor were determined for the azide complex for comparison with those for the cyanide complex. Comparison of the predicted and observed dipolar shifts reveals that shift differences are strongly dominated by differences in electronic structure and do not provide any evidence for detectable differences in molecular structure or hydrogen bonding except in the immediate vicinity of the distal ligand. The readily cleaved C-terminus interacts with the active site and saturation-transfer allows difficult heme assignments in the high-spin aquo complex.
authors.affiliation: Department of Chemistry, University of California, Davis, CA 95616, United States.
authors.forename: Li-Hua
authors.initials: LH
authors.lastname: Ma
authors.forename: Yangzhong
authors.initials: Y
authors.lastname: Liu
authors.forename: Xuhong
authors.initials: X
authors.lastname: Zhang
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yoshida
authors.forename: Gerd N
authors.initials: GN
authors.lastname: La Mar
mesh_terms: D001386:Azides / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D003486:Cyanides / Q000737:chemistry*; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry* / Q000378:metabolism; D006427:Hemin / Q000737:chemistry* / Q000378:metabolism; D006860:Hydrogen Bonding; D008024:Ligands; D009345:Neisseria meningitidis / Q000201:enzymology*; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation
chemical_list: D001386:Azides; D001426:Bacterial Proteins; D003486:Cyanides; D008024:Ligands; D006427:Hemin; C423452:HemO protein, Neisseria meningitidis; D006419:Heme Oxygenase (Decyclizing)