화학공학소재연구정보센터
Inorganic Chemistry, Vol.55, No.4, 1613-1622, 2016
Effects of Heme Electronic Structure and Distal Polar Interaction on Functional and Vibrational Properties of Myoglobin
We analyzed the oxygen (O-2) and carbon monoxide (CO) binding properties, autoxidation reaction rate, and FeO2 and FeCO vibrational frequencies of the H64Q mutant of sperm whale myoglobin (Mb) reconstituted with chemically modified heme cofactors possessing a variety of heme Fe electron densities (rho(Fe)), and the results were compared with those for the previously studied native [Shibata, T. et al. J. Am. Chem. Soc. 2010, 132, 6091-6098], and H64L [Nishimura, R. et al. Inorg. Chem. 2014, S3, 1091-1099], and L29F [Nishimura, R. et al. Inorg. Chem. 2014, 53, 9156-9165] mutants in order to elucidate the effect of changes in the heme electronic structure and distal polar interaction contributing to stabilization of the Fe-bound ligand on the functional and vibrational properties of the protein. The study revealed that, as in the cases of the previously studied native protein [Shibata, T. et al. Inorg. Chem. 2012, 51, 11955-11960], the O-2 affinity and autoxidation reaction rate of the H64Q mutant decreased with a decrease in rho(Fe) as expected from the effect of a change in rho(Fe) on the resonance between the Fe2+-O-2 bond and Fe3+-O-2-like species in the O-2 form, while the CO affinity of the protein is independent of a change in rho(Fe). We also found that the well-known inverse correlation between the frequencies of Fe-bound CO (nu(CO)) and Fe-C (nu(FeC)) stretching [Li, X.-Y.; Spiro, T. G. J. Am. Chem. Soc. 1988, 110, 6024-6033] is affected differently by changes in rho(Fe) and the distal polar interaction, indicating that the effects of the two electronic perturbations due to the chemical modification of a heme cofactor and the replacement of nearby amino acid residues on the resonance between the two alternative canonical forms of the FeCO fragment in the protein are slightly different from each other. These findings provide a new insight for deeper understanding of the functional regulation of the protein.