Chlorosome Proteins Studied by MALDI-TOF-MS: Topology of CsmA in Chlorobium tepidum |
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Authors: | Kirstin J. Milks Marianne Danielsen Søren Persson Ole Nørregaard Jensen Raymond P. Cox Mette Miller |
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Affiliation: | (1) Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark |
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Abstract: | Chlorosomes, the light-harvesting apparatus of green bacteria, are a unique antenna system, in which pigments are organized in aggregates rather than associated with proteins. Isolated chlorosomes from the green sulphur bacterium Chlorobium tepidum contain 10 surface-exposed proteins. Treatment of chlorosomes from Chlorobium tepidum with protease caused changes in the spectral properties of bacteriochlorophyll c and digestion of chlorosome proteins. Using SDS-PAGE analysis, immunoblotting and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) we have investigated the topology of the 59-residue CsmA protein. Our results show that at the N-terminus, the only amino acid available for protease degradation is the methionine. At the C-terminus, amino acids can be removed by protease treatment to produce a residual protein containing at least the sequence between residues 2 and 38. These results indicate that the N-terminal portion of the CsmA protein, which is predicted to be mainly hydrophobic, is buried in the chlorosome envelope. |
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Keywords: | chlorosomes CsmA green bacteria MALDI-TOF-MS |
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