On Excitation Energy Transfer within the Baseplate BChl a-CsmA Complex of Chloroflexus aurantiacus

J Phys Chem B. 2019 Nov 21;123(46):9786-9791. doi: 10.1021/acs.jpcb.9b08043. Epub 2019 Nov 11.

Abstract

Recently, a hybrid approach combining solid-state NMR spectroscopy and cryo-electron microscopy showed that the baseplate in green sulfur bacterium Chlorobaculum tepidum is a 2D lattice of BChl a-CsmA dimers [Nielsen, J. T.; et al., Nat. Commun. 2016, 7, 12454-12465]. While the existence of the BChl a-CsmA subunit was previously known, the proposed orientations of the BChl a pigments had only been elucidated from spectral data up to this point. Regarding the electronic structure of the baseplate, two models have been proposed. 2D electronic spectroscopy data were interpreted as revealing that at least four excitonically coupled BChl a might be in close contact. Conversely, spectral hole burning data suggested that the lowest energy state was localized, yet additional states are sometimes observed because of the presence of the Fenna-Matthews-Olson (FMO) antenna protein. To solve this conundrum, this work studies the chlorosome-baseplate complex from Chloroflexus aurantiacus, which does not contain the FMO protein. The results confirm that in both C. tepidum and C. aurantiacus, excitation energy is transferred to a localized low-energy trap state near 818 nm with similar rates, most likely via exciton hopping.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Bacteriochlorophylls / chemistry*
  • Bacteriochlorophylls / metabolism
  • Chloroflexus / metabolism*
  • Energy Transfer*
  • Light-Harvesting Protein Complexes / chemistry
  • Light-Harvesting Protein Complexes / metabolism
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism
  • Temperature

Substances

  • Bacterial Proteins
  • Bacteriochlorophylls
  • FMO bacteriochlorophyll protein, Bacteria
  • Light-Harvesting Protein Complexes
  • Protein Subunits
  • bacteriochlorophyll c

Supplementary concepts

  • Chloroflexus aurantiacus