Journal article
Characterization of pH-dependent conformation heterogeneity in Rhodospirillum rubrum cytochrome c2 using nitrogen-15 and proton NMR
Biochemistry (Easton), Vol.29(12), pp.2920-2925
03/01/1990
DOI: 10.1021/bi00464a005
Abstract
The 15N-enriched ferricytochrome c2 from Rhodospirillum rubrum has been studied by 15N and ’H NMR spectroscopy as a function of pH. The 15N resonances of the heme and ligand t nitrogen are broadened beyond detection because of paramagnetic relaxation. The 15N resonance of the ligand histidine π nitrogen was unambiguously identified at 184 ppm (pH 5.6). The 15N resonances of the single nonligand histidine are observed only at low pH, as in the ferrocytochrome because of the severe broadening caused by tautomerization. The dependence of the 15N and ’H spectra of the ferricytochrome on pH indicated that the ligand histidine it NH does not dissociate in the neutral pH range and is involved in a hydrogen bond, similar to that in the reduced state. Because neither deprotonated nor non-hydrogen-bonded forms of the ligand histidine are observed in the spectra of either oxidation state, the participation of such forms in producing heterogeneous populations having different electronic g tensors is ruled out. Transitions having pATa's of 6.2, 8.6, and 9.2 are observed in the ferricytochrome. The localized conformational change around the Ω loops is observed in the neutral pH range, as in the ferrocytochrome. Structural heterogeneity leads to multiple resonances of the heme ring methyl at position 8. The exchange rate between the conformations is temperature dependent. The transition with a pKa of 6.2 is assigned to the His-42 imidazole group. The displacement of the ligand methionine, which occurs with a pKa of 9.2, causes gross conformational change near the heme center. There are multiple conformations at high pH, only one of which is able to transfer electrons efficiently, as judged by saturation-transfer experiments. The N-terminus of the ferricytochrome has a pKa of 8.6. In contrast to its partially restricted mobility in the reduced state, it is found to be very mobile, reflecting a looser structure of the ferricytochrome
Details
- Title: Subtitle
- Characterization of pH-dependent conformation heterogeneity in Rhodospirillum rubrum cytochrome c2 using nitrogen-15 and proton NMR
- Creators
- Liping P YuGary M Smith
- Resource Type
- Journal article
- Publication Details
- Biochemistry (Easton), Vol.29(12), pp.2920-2925
- Publisher
- American Chemical Society
- DOI
- 10.1021/bi00464a005
- ISSN
- 0006-2960
- eISSN
- 1520-4995
- Language
- English
- Date published
- 03/01/1990
- Academic Unit
- Biochemistry and Molecular Biology; Medicine Administration
- Record Identifier
- 9984627286202771
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