Journal
BIOCHEMISTRY
Volume 47, Issue 5, Pages 1435-1441Publisher
AMER CHEMICAL SOC
DOI: 10.1021/bi701616r
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Green sulfur bacteria possess two light-harvesting antenna systems, the chlorosome and the. Fenna-Matthews-Olson (FMO) protein. In addition to self-aggregated bacteriochlorophyll (BChl) c, chlorosomes of Chlorobium tepidum contain a small amount of BChl a (ratio 100:1). The chlorosomal BChl a is associated with CsmA, a 6.2 kDa protein that accounts for more than 50% of the protein content of chlorosomes. This CsmA-BChl a complex is located in the chlorosome baseplate with the hydrophilic C-terminal part of CsmA in contact with the FMO protein. CsmA was purified from Chl. tepidum. Isolated chlorosomes were lyophilized and extracted with chloroform/methanol (1:1, v/v). The extract was further purified using gel filtration and reverse-phase HPLC and the purity of the preparation confirmed by SDS-PAGE. Mass spectrometric analysis showed an m/z of 6154.8, in agreement with the calculated mass of the csmA gene product after C-terminal processing. CD spectroscopy of the isolated protein showed that the main structural motif was an a-helix. We have reconstituted the isolated CsmA protein with BChl a in micelles of n-octyl beta-D-glucopyranoside. The resulting preparation reproduced the spectral characteristics of the CsmA-BChl a complex present in the chlorosome baseplate.
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