Alteration of axial coordination by protein engineering in myoglobin. Bisimidazole ligation in the His64-->Val/Val68-->His double mutant.Dou, Y., Admiraal, S.J., Ikeda-Saito, M., Krzywda, S., Wilkinson, A.J., Li, T., Olson, J.S., Prince, R.C., Pickering, I.J., George, G.N.
(1995) J.Biol.Chem. 270: 15993-16001
- PubMed: 7608158
- DOI: 10.1074/jbc.270.27.15993
- PubMed Abstract:
- Distal Pocket Polarity in Ligand Binding to Myoglobin: Deoxy and Carbonmonoxy Forms of Threonine68(E11) Mutant Investigated by X-Ray Crystallography and Infrared Spectroscopy
Cameron, A.D.,Smerdon, S.J.,Wilkinson, A.J.,Habash, J.,Helliwell, J.R.,Li, T.,Olson, J.S.
(1993) Biochemistry 32: 13061
- High Resolution X-Ray Structures of Pig Metmyoglobin and Two Cd3 Mutants Mb(Lys45-->Arg) and Mb(Lys45-->Ser)
Oldfield, T.J.,Smerdon, S.J.,Dauter, Z.,Petratos, K.,Wilson, K.S.,Wilkinson, A.J.
(1992) Biochemistry 31: 8732
- Determination of the Crystal Structure of Recombinant Pig Myoglobin by Molecular Replacement and its Refinement
Smerdon, S.J.,Oldfield, T.J.,Dodson, E.J.,Dodson, G.G.,Hubbard, R.E.,Wilkinson, A.J.
(1990) Acta Crystallogr.,Sect.B 46: 370
Pig and human myoglobin have been engineered to reverse the positions of the distal histidine and valine (i.e. His64(E7)-->Val and Val68(E11)-->His). Spectroscopic and ligand binding properties have been measured for human and pig H64V/V68H myoglobin ...
Pig and human myoglobin have been engineered to reverse the positions of the distal histidine and valine (i.e. His64(E7)-->Val and Val68(E11)-->His). Spectroscopic and ligand binding properties have been measured for human and pig H64V/V68H myoglobin, and the structure of the pig H64V/V68H double mutant has been determined to 2.07-A resolution by x-ray crystallography. The crystal structure shows that the N epsilon of His68 is located 2.3 A away from the heme iron, resulting in the formation of a hexacoordinate species. The imidazole plane of His68 is tilted relative to the heme normal; moreover it is not parallel to that of His93, in agreement with our previous proposal (Qin, J., La Mar, G. N., Dou, Y., Admiraal, S. J., and Ikeda-Saito, M. (1994) J. Biol. Chem. 269, 1083-1090). At cryogenic temperatures, the heme iron is in a low spin state, which exhibits a highly anisotropic EPR spectrum (g1 = 3.34, g2 = 2.0, and g3 < 1), quite different from that of the imidazole complex of metmyoglobin. The mean iron-nitrogen distance is 2.01 A for the low spin ferric state as determined by x-ray spectroscopy. The ferrous form of H64V/V68H myoglobin shows an optical spectrum that is similar to that of b-type cytochromes and consistent with the hexacoordinate bisimidazole hemin structure determined by the x-ray crystallography. The double mutation lowers the ferric/ferrous couple midpoint potential from +54 mV of the wild-type protein to -128 mV. Ferrous H64V/V68H myoglobin binds CO and NO to form stable complexes, but its reaction with O2 results in a rapid autooxidation to the ferric species. All of these results demonstrate that the three-dimensional positions of His64 and Val68 in the wild-type myoglobin are as important as the chemical nature of the side chains in facilitating reversible O2 binding and inhibiting autooxidation.
Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4970, USA.