A hybrid approach combining solid-state NMR spectroscopy and cryo-electron microscopy showed recently that the baseplate in the green sulfur bacterium Chlorobaculum (Cb.) tepidum is a 2D lattice of BChl a–CsmA dimers. Previous 2D electronic spectroscopy data, however, implied that at least four excitonically coupled BChl a might be in close contact within the baseplate structure. We argued that the four excitonic states assigned to coupled BChl a within the CsmA protein could be due to the contamination with the FMO antenna. To solve this conundrum, we studied the chlorosome-baseplate complex from Chloroflexus (Cfx.) aurantiacus, which by its nature does not contain the FMO antenna. We confirm that in both Cb. tepidum and Cfx. aurantiacus, excitation energy is transferred to a localized low-energy trap state near 818 nm with similar rates, most likely via exciton hopping. This result is consistent with a disordered two-dimensional lattice of CsmA protein dimers containing two BChl a molecules sandwiched between the protein hydrophobic regions.

Excitonic structure in the baseplate complex of Chloroflexus (Cfx.) aurantiacus and Cb. tepidum

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.