Atomic structure of the bacteriochlorophyll c assembly in intact chlorosomes from Chlorobium limicola determined by solid-state NMR
Green sulfur photosynthetic bacteria optimize their antennas, chlorosomes, especially for harvesting weak light by organizing bacteriochlorophyll (BChl) assembly without any support of proteins. As it is difficult to crystallize the organelles, a high-resolution structure of the light-harvesting devices in the chlorosomes has not been clarified. We have determined the structure of BChl c assembly in the intact chlorosomes from Chlorobium limicola on the basis of 13C dipolar spin-diffusion solid-state NMR analysis of uniformly 13C-labeled chlorosomes. About 90 intermolecular C–C distances were obtained by the simultaneous assignment of distance correlations and the structure optimization preceded by the polarization-transfer matrix analysis. An atomic structure was obtained, using these distance constraints. The determined structure of the chlorosomal BChl c assembly is built with the parallel layers of piggyback-dimers. This supramolecular structure would provide insights into the mechanism of weak-light capturing.
KeywordsLight-harvesting unit 13C-labeled chlorosome Supramolecular structure Proton-driven spin diffusion Simulated anneal molecular dynamics Piggyback-dimer
We are grateful to Prof. Yasushi Koyama (Kwansei Gakuin University) for the long-standing collaboration also to Drs. Yoshinori Kakitani (Kwansei Gakuin University) and Tadashi Mizoguchi (Ritsumeikan University) for performing this study together. This study was partly supported by the Grants-in-Aid for Scientific Research on Priority Area from the Ministry of Education, Culture, Sports, Science, and Technology of Japan, and by grants from the Japan New Energy and Industrial Technology Development Organization.
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