Quinone (QB) Binding Site and Protein Stuctural Changes in Photosynthetic Reaction Center Mutants at Pro-L209 Revealed by Vibrational Spectroscopy
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- 作者：Eliane Nabedryk ; Jacques Breton ; Pierre Sebban ; and Laura Baciou
- 刊名：Biochemistry
- 出版年：2003
- 出版时间：May 20, 2003
- 年：2003
- 卷：42
- 期：19
- 页码：5819 - 5827
- 全文大小：149K
- 年卷期：v.42,no.19(May 20, 2003)
- ISSN：1520-4995
文摘
The effect of substituting Pro-L209 with Tyr, Phe, Glu, and Thr in photosynthetic reactioncenters (RCs) from Rhodobacter sphaeroides was investigated by monitoring the light-induced FTIRabsorption changes associated with the photoreduction of the secondary quinone QB. Pro-L209 is close toa chain of ordered water molecules connecting QB to the bulk phase. In wild-type RCs, two distinct mainQB binding sites (distal and proximal to the non-heme iron) have been described in the literature. TheX-ray structures of the mutant RCs Pro-L209 
Tyr, Pro-L209 Phe, and Pro-L209 Glu have revealedthat QB occupies a proximal, intermediate, and distal position, respectively [Kuglstatter, A., Ermler, U.,Michel, H., Baciou, L., and Fritzsch, G. (2001) Biochemistry 40, 4253-4260]. FTIR absorption changesassociated with the reduction of QB in Pro-L209 Phe RCs reconstituted with 13C-labeled ubiquinoneshow a highly specific IR fingerprint for the C=O and C=C modes of QB upon selective labeling at C1or C4. This IR fingerprint is similar to those of wild-type RCs and the Pro-L209 Tyr mutant [Breton,J., Boullais, C., Mioskowski, C., Sebban, P., Baciou, L., and Nabedryk, E. (2002) Biochemistry 41, 12921-12927], demonstrating that equivalent interactions occur between neutral QB and the protein in wild-typeand mutant RCs. It is concluded that in all RCs, neutral QB in its functional state occupies a uniquebinding site which is favored to be the proximal site. This result contrasts with the multiple QB bindingsites found in crystal structures. With respect to wild-type RCs, the largest FTIR spectral changes uponQB- formation are observed for the Phe-L209 and Tyr-L209 mutants which undergo similar proteinstructural changes and perturbations of the semiquinone modes. Smaller changes are observed for theGlu-L209 mutant, while the vibrational properties of the Thr-L209 mutant are essentially the same asthose for native RCs.
Tyr, Pro-L209 Phe, and Pro-L209 Glu have revealedthat QB occupies a proximal, intermediate, and distal position, respectively [Kuglstatter, A., Ermler, U.,Michel, H., Baciou, L., and Fritzsch, G. (2001) Biochemistry 40, 4253-4260]. FTIR absorption changesassociated with the reduction of QB in Pro-L209 Phe RCs reconstituted with 13C-labeled ubiquinoneshow a highly specific IR fingerprint for the C=O and C=C modes of QB upon selective labeling at C1or C4. This IR fingerprint is similar to those of wild-type RCs and the Pro-L209 Tyr mutant [Breton,J., Boullais, C., Mioskowski, C., Sebban, P., Baciou, L., and Nabedryk, E. (2002) Biochemistry 41, 12921-12927], demonstrating that equivalent interactions occur between neutral QB and the protein in wild-typeand mutant RCs. It is concluded that in all RCs, neutral QB in its functional state occupies a uniquebinding site which is favored to be the proximal site. This result contrasts with the multiple QB bindingsites found in crystal structures. With respect to wild-type RCs, the largest FTIR spectral changes uponQB- formation are observed for the Phe-L209 and Tyr-L209 mutants which undergo similar proteinstructural changes and perturbations of the semiquinone modes. Smaller changes are observed for theGlu-L209 mutant, while the vibrational properties of the Thr-L209 mutant are essentially the same asthose for native RCs.