de Groot H J, Gebhard R, van der Hoef I, Hoff A J, Lugtenburg J, Violette C A, Frank H A
Department of Chemistry, Gorlaeus Laboratories, Leiden, The Netherlands.
Biochemistry. 1992 Dec 15;31(49):12446-50. doi: 10.1021/bi00164a021.
The photosynthetic reaction center of Rhodobacter sphaeroides 2.4.1 contains one carotenoid that protects the protein complex against photodestruction. The structure around the central (15,15') double bond of the bound spheroidene carotenoid was investigated with low-temperature magic angle spinning 13C NMR, which allows an in situ characterization of the configuration of the central double bond in the carotenoid. Carotenoidless reaction centers of R. sphaeroides R26 were reconstituted with spheroidene specifically labeled at the C-14' or C-15' position, and the signals from the labels were separated from the natural abundance background using 13C MAS NMR difference spectroscopy. The resonances shift 5.2 and 3.8 ppm upfield upon incorporation in the protein complex, similar to the 5.6 and 4.4 ppm upfield shift occurring in the model compound beta-carotene upon trans to 15,15'-cis isomerization. Hence the MAS NMR favors a cis configuration, as opposed to the trans configuration deduced from X-ray data.
球形红杆菌2.4.1的光合反应中心含有一种类胡萝卜素，可保护蛋白质复合物免受光破坏。利用低温魔角旋转13C NMR研究了结合的球形烯类胡萝卜素中心（15,15'）双键周围的结构，该技术能够对类胡萝卜素中心双键的构型进行原位表征。用在C-14'或C-15'位置特异性标记的球形烯对球形红杆菌R26的无类胡萝卜素反应中心进行重构，并使用13C MAS NMR差谱将标记信号与天然丰度背景分离。在并入蛋白质复合物后，共振信号分别上移5.2和3.8 ppm，类似于模型化合物β-胡萝卜素从反式到15,15'-顺式异构化时发生的5.6和4.4 ppm上移。因此，与X射线数据推断的反式构型相反，MAS NMR支持顺式构型。
