Alternative Excitonic Structure in the Baseplate (BChl a-CsmA Complex) of the Chlorosome from Chlorobaculum tepidum.
In the photosynthetic green sulfur bacterium Chlorobaculum tepidum, the baseplate mediates excitation energy transfer from the light-harvesting chlorosome to the Fenna-Matthews-Olson (FMO) complex and subsequently toward the reaction center (RC). Literature data suggest that the baseplate is a 2D lattice of BChl a-CsmA dimers. However, recently, it has been proposed, using 2D electronic spectroscopy (2DES) at 77 K, that at least four excitonically coupled BChl a are in close contact within the baseplate structure [ Dostál , J. ; et al., J. Phys. Chem. Lett. 2014 , 5 , 1743 ]. This finding is tested via hole burning (HB) spectroscopy (5 K). Our results indicate that the four excitonic states identified by 2DES likely correspond to contamination of the baseplate with the FMO antenna and possibly the RC. In contrast, HB reveals a different excitonic structure of the baseplate chromophores, where excitation is transferred to a localized trap state near 818 nm via exciton hopping, which leads to emission near 826 nm.
Adam
A
Kell
Jinhai
J
Chen
Mahboobe
M
Jassas
‡Department of Chemistry and Biochemistry, Clark University, Worcester, Massachusetts 01610, United States.
Joseph Kuo-Hsiang
JK
Tang
Ryszard
R
Jankowiak
D001426:Bacterial Proteins / Q000737:chemistry*; D019414:Chlorobi / Q000737:chemistry* / Q000166:cytology; D004735:Energy Transfer; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D011487:Protein Conformation; D013057:Spectrum Analysis
D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes
BChl a; Fenna−Matthews− Olson complex; baseplate chromophore; hole burning spectroscopy