Effect of the distal residues on the vibrational modes of the Fe-CO bond in hemoglobin studied by protein engineering
- Georgia Institute of Technology, Atlanta (USA)
- Medical Research Council Laboratory of Molecular Biology, Cambridge (England)
Using an Escherichia coli gene expression system, the authors have engineered human hemoglobin (Hb) mutants having the distal histidine (E7) and valine (E11) residues replaced by other amino acids. The interaction between the mutated distal residues and bound carbon monoxide has been studied by Soret-excited resonance Raman spectroscopy. The replacement of Val-E11 by Ala, Leu, Ile, and Met has no effect on the {nu}(C-O), {nu}(Fe-CO) stretching or {delta}(Fe-C-O) bending frequencies in both the {alpha} and {beta} subunits of Hb, although some of these mutations affect the CO affinity as much as 40-fold. The strain imposed on the protein by the binding of CO is not localized in the Fe-CO bond and is probably distributed among many bonds in the globin. The replacement of His-E7 by Val or Gly brings the stretching frequencies {nu}(Fe-CO) and {nu}(C-O) close to those of free heme complexes. In contrast, the substitution of His-E7 by Gln, which is flexible and polar, produces no effects on the resonance Raman spectrum of either {alpha}- or {beta}-globin. The replacement of His-E7 of {beta}-globin by Phe shows the same effect as replacement by Gly or Val. Therefore, the steric bulk of the distal residues is not the primary determinant of the Fe-CO ligand vibrational frequencies. The ability of both histidine and glutamine to alter the {nu}(C-O), {nu}(Fe-CO), or {delta}(Fe-C-O) frequencies may be attributed to the polar nature of their side chains which can interact with bound CO in a similar manner.
- OSTI ID:
- 5394513
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 29:23; ISSN 0006-2960; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
AZOLES
BACTERIA
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CARBOXYLIC ACIDS
CHALCOGENIDES
CHEMICAL BONDS
ENERGY LEVELS
ESCHERICHIA COLI
EXCITED STATES
GLOBINS
HEMOGLOBIN
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HISTIDINE
IMIDAZOLES
LASER SPECTROSCOPY
MICROORGANISMS
MUTANTS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PIGMENTS
PORPHYRINS
PROTEIN ENGINEERING
PROTEINS
RAMAN SPECTROSCOPY
SPECTROSCOPY
VALINE
VIBRATIONAL STATES