A heme c-peptide model system for the resonance Raman study of c-type cytochromes: Characterization of the solvent-dependence of peptide-histidine-heme interactions

Abstract

The visible absorption and Soret-excited resonance Raman spectra of ferrous microperoxidase-8 [MP8(II)], an octapeptide containing a heme c, are reported. These spectroscopies indicate that MP8(II), dissolved in aqueous buffered solutions, forms low-spin six-coordinated complexes in the 7-14 pH range. Intermolecular bonding interactions of MP8(II) in water account for this behavior. On the contrary, when the hemopeptide is dispersed in aqueous solutions containing detergent or an alcohol, the spectroscopic data show that the iron atom of MP8(II) is essentially high-spin five-coordinated in accordance with a monomeric structure of MP8(II). In addition to a high-spin signature to the heme skeletal modes, the high-frequency regions of resonance Raman spectra characterize an electronic influence of the thioether bridges on the frequency of stretching modes of C beta-C beta bonds (nu 2, nu 11, and nu 29). On the other hand, the low-frequency Raman spectra of monomeric MP8(II) at pH 7.5 present significant differences in the 150-250-cm-1 regions depending upon the solvent composition (pH, presence or absence of detergent, alcohol). These effects are attributed to frequency variations of the Fe-N(His)-involving mode which indicate changes in the H-bonding interactions of the axial His and therefore solvent-dependent changes of the octapeptide conformation. Our resonance Raman data further show that the axial His of monomeric MP8(II) could be totally deprotonated in aqueous cetyltrimethylammonium bromide solution at very alkaline pH (pKa = 13.3). The vibrational data (100-1700 cm-1) obtained for the various monomeric forms of MP8(II) are expected to be useful for determining the heme structure and environment in reduced c'-type cytochromes. Comparisons of resonance Raman data with X-ray crystallographic data available for different hemoproteins allow us to evaluate the ionization and H-bonding states of the His bound to the high-spin five-coordinated hemes. These data are discussed in terms of proximal influence of protein-His-heme interactions on the determination and the regulation of a particular biological function.

Structural changes and picosecond to second dynamics of cytochrome c in interaction with nitric oxide in ferrous and ferric redox states

“…1a). Similar frequency downshifts of the mode ν 3 were also observed for other 5c-HS species like microperoxidase 36 or a fragment of ferrous Cyt c. 62 Similarly, the mode ν 2 at 1590 cm -1 shifts to 1578 cm -1 and simultaneously decreases in intensity as observed for myoglobin. 60 Lastly, the band ν 10 at 1631 cm -1 disappears, in agreement with the high spin nature of the heme after NO dissociation.…”

The Critical Role of the Proximal Calcium Ion in the Structural Properties of Horseradish Peroxidase

“…Furthermore, it demonstrates that substantial structural changes of the heme environment in the vicinity of the proximal histidine are induced by Ca 2ϩ depletion. In fact, the Fe-Im stretching frequency occurs at 220 cm Ϫ1 in myoglobin, where the proximal His is hydrogen-bonded with a neutral peptide carbonyl group (49), and at 196 cm Ϫ1 in the Fe 2ϩ protoporphyrin IX histidine complex, where the proximal His is not involved in hydrogen bonding interactions (50). In this context, it should be recalled that the residue adjacent to the proximal His (Thr 171 ) provides two coordination bonds to the proximal Ca 2ϩ ion ( Fig.…”

Miniaturized hemoproteins

“…However, their stability is interpretation of some spectroscopic properties of synthetic heme-peptide adducts. 75 higher than that of simple protoporphyrin systems, thus indicating that the presence of a small peptide chain can play an important protective role. Recently, 74 the influence of peptide chain length and…”