A reconstituted light-harvesting complex from the green sulfur bacterium Chlorobium tepidum containing CsmA and bacteriochlorophyll a.
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 alpha-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.
Pedersen
Marie Ø
MØ
Department of Chemistry, University of Aarhus, Denmark.
Pham
Lan
L
Steensgaard
Dorte B
DB
Miller
Mette
M
D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification; D025541:Bacteriochlorophyll A / Q000737:chemistry*; D041883:Chlorobium / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008823:Micelles; D013055:Spectrophotometry, Infrared
D001426:Bacterial Proteins; D025541:Bacteriochlorophyll A; C404706:CsmA protein, Chlorobium tepidum; D045342:Light-Harvesting Protein Complexes; D008823:Micelles