1mni
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(New page: 200px<br /><applet load="1mni" size="450" color="white" frame="true" align="right" spinBox="true" caption="1mni, resolution 2.07Å" /> '''ALTERATION OF AXIAL ...)
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ALTERATION OF AXIAL COORDINATION BY PROTEIN ENGINEERING IN MYOGLOBIN. BIS-IMIDAZOLE LIGATION IN THE HIS64-->VAL(SLASH)VAL68-->HIS DOUBLE MUTANT
Overview
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.
About this Structure
1MNI is a Single protein structure of sequence from Sus scrofa with HEM as ligand. Full crystallographic information is available from OCA.
Reference
Alteration of axial coordination by protein engineering in myoglobin. Bisimidazole ligation in the His64-->Val/Val68-->His double mutant., Dou Y, Admiraal SJ, Ikeda-Saito M, Krzywda S, Wilkinson AJ, Li T, Olson JS, Prince RC, Pickering IJ, George GN, J Biol Chem. 1995 Jul 7;270(27):15993-6001. PMID:7608158
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