NMR determination of the orientation of the magnetic susceptibility tensor in cyanometmyoglobin: A new probe of steric tilt of bound ligand

Journal Article · Tue Feb 13 00:00:00 EST 1990 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00458a029· OSTI ID:6828874

Emerson, S D; La Mar, G N ^[1]

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1. Univ. of California, Davis (USA)

The experimentally determined paramagnetic dipolar shifts for noncoordinated amino acid side-chain protons in the heme pocket of sperm whale cyanometmyoglobin were used to determine in solution the orientation of the principal axes for the paramagnetic susceptibility tensor relative to the heme iron molecular coordinates. The determination was made by a least-squares search for the unique Euler rotation angles which convert the geometric factors in the molecular (crystal) coordinates to ones that correctly predict each of 41 known dipolar shifts by using the magnetic anisotropies computed previously. An excellent fit to experimental shifts was obtained, which also provided predictions that allowed subsequent new assignments to be made. The magnetic axes are oriented so that the z axis is tipped {approximately}15{degree} from the heme normal toward the heme {delta}-meso-H and coincides approximately with the characterized FeCO tilt axis in the isostructural MbCO complex. Since the FeCO and FeCN units are isostructural, the authors propose that the dominant protein constraint that tips the magnetic z axis from the heme normal is the tilt of the FeCN by steric interactions with the distal residues. It is shown that the proximal His ring nonlabile proton hyperfine shifts provide direct and exquisitely sensitive indicators of the degree of the z axis tilt that may serve as a valuable probe for characterizing variable steric interactions in the distal pocket of both point mutants and natural genetic variants of myoglobin.

• OSTI ID: 6828874
• Journal Information: Biochemistry; (USA), Vol. 29:6; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
HEME
CHEMICAL SHIFT
MYOGLOBIN
NUCLEAR MAGNETIC RESONANCE
CYANIDES
HEAVY WATER
HYPERFINE STRUCTURE
MOLECULAR STRUCTURE
PARAMAGNETISM
STEREOCHEMISTRY
CARBOXYLIC ACIDS
GLOBINS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
MAGNETIC RESONANCE
MAGNETISM
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN COMPOUNDS
PIGMENTS
PORPHYRINS
PROTEINS
RESONANCE
WATER
550201* - Biochemistry- Tracer Techniques