Stereochemical conversion of C3-vinyl group to 1-hydroxyethyl group in bacteriochlorophyll c by the hydratases BchF and BchV: adaptation of green sulfur bacteria to limited-light environments.
Photosynthetic green sulfur bacteria inhabit anaerobic environments with very low-light conditions. To adapt to such environments, these bacteria have evolved efficient light-harvesting antenna complexes called as chlorosomes, which comprise self-aggregated bacteriochlorophyll c in the model green sulfur, bacterium Chlorobaculum tepidum. The pigment possess a hydroxy group at the C3(1) position that produces a chiral center with R- or S-stereochemistry and the C3(1) -hydroxy group serves as a connecting moiety for the self-aggregation. Chlorobaculum tepidum carries the two possible homologous genes for C3-vinyl hydratase, bchF and bchV. In the present study, we constructed deletion mutants of each of these genes. Pigment analyses of the bchF-inactivated mutant, which still has BchV as a sole hydratase, showed higher ratios of S-epimeric bacteriochlorophyll c than the wild-type strain. The heightened prevalence of S-stereoisomers in the mutant was more remarkable at lower light intensities and caused a red shift of the chlorosomal Qy absorption band leading to advantages for light-energy transfer. In contrast, the bchV-mutant possessing only BchF showed a significant decrease of the S-epimers and accumulations of C3-vinyl BChl c species. As trans- criptional level of bchV was upregulated at lower light intensity, the Chlorobaculum tepidum adapted to low-light environments by control of the bchV transcription.
Department of Medical Biochemistry, Kurume University School of Medicine, Kurume, Fukuoka, 830-0011, Japan.
Jiro
J
Harada
Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan.
Misato
M
Teramura
Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan.
Tadashi
T
Mizoguchi
Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo, 152-8550, Japan.|PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama, 332-0012, Japan.
Yusuke
Y
Tsukatani
Department of Medical Biochemistry, Kurume University School of Medicine, Kurume, Fukuoka, 830-0011, Japan.
Ken
K
Yamamoto
Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan.
Hitoshi
H
Tamiaki
D000222:Adaptation, Physiological / Q000235:genetics; D001426:Bacterial Proteins / Q000378:metabolism*; D001429:Bacteriochlorophylls / Q000378:metabolism*; D019414:Chlorobi / Q000235:genetics* / Q000378:metabolism*; D003593:Cytoplasm; D000431:Ethanol / Q000378:metabolism*; D005798:Genes, Bacterial; D006867:Hydrolases / Q000378:metabolism*; D008027:Light; D015388:Organelles / Q000378:metabolism; D010788:Photosynthesis; D017384:Sequence Deletion; D013237:Stereoisomerism
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; C065424:1-hydroxyethyl radical; D000431:Ethanol; C002084:bacteriochlorophyll c; D006867:Hydrolases