C magic angle spinning NMR characterization of the functionally asymmetric Q{sub A} binding in Rhodobacter sphaeroides R26 photosynthetic reaction centers using site-specific {sup 13}C-labeled ubiqinone-10
- Leiden Univ. (Netherlands); and others
Photosynthetic reaction centers (RCs) of Rhodobacter sphaeroides R26 were reconstituted at the Q{sub A} site with ubiquinone-10, selectively {sup 13}C-enriched on positions 1, 2, 3, 4, and 3-Me (IUPAC numbering). RCs dispersed in LDAO detergent were studied with {sup 13}C CP/MAS NMR spectroscopy at temperatures between 180 and 240 K, while RCs precipitated by removal of the detergent were investigated at ambient temperature and at temperatures down to 180 K. Electrostatic charge differences in Q{sub A} induced by polarization from the protein are less than 0.02 electronic equivalent for any of the labeled positions. This includes the 4-carbonyl, which is therefore not significantly polarized by an electrostatic binding interaction with the protein. The Q{sub A} site is slightly heterogeneous on the scale of the NMR as the observed line widths of the labels are between 150 and 300 Hz and inhomogeneous broadening is observed for the signals of positions 1, 2, and 3 upon cooling. The chemical shifts are 184, 144, and 137 ppm for the labels at positions 1, 2, 3, and 12 ppm for the 3-methyl {sup 13}C. For the 4-carbonyl only at sample temperatures below {approximately}255 K a CP/MAS response can be observed at 183 ppm. The principal components of the chemical shift tensors for the ring labels in Q{sub A} were estimated using difference spectroscopy. Although the asymmetry of the anisotropy of the 4-{sup 13}C signal from Q{sub A} is Only moderately different from the anisotropy of the 4 position in crystalline UQ{sub 10}, it is concluded that the NMR is compatible with a decrease of the 4 C{double_bond}O bond order upon binding to the protein. The temperature-dependent asymmetry between the two carbonyls in Q{sub A} indicates that the putative strong interaction with the protein at position 4 involves dynamic character, which may be of importance to the specific Q{sub A} redox chemistry. 53 refs., 6 figs., 2 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 245277
- Journal Information:
- Biochemistry (Eaton), Vol. 34, Issue 32; Other Information: PBD: 15 Aug 1995
- Country of Publication:
- United States
- Language:
- English
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