TY - JOUR
T1 - Bacteriochlorophyllide c C-82 and C-121 methyltransferases are essential for adaptation to low light in Chlorobaculum tepidum
AU - Gomez Maqueo Chew, Aline
AU - Frigaard, Niels-Ulrik
AU - Bryant, Donald A
N1 - Keywords: Adaptation, Physiological; Bacterial Proteins; Bacteriochlorophylls; Chlorobi; Chlorophyllides; Cytoplasm; Gene Deletion; Methyltransferases; Microscopy, Electron, Transmission; Mutagenesis, Insertional; Organelles; Spectrum Analysis
PY - 2007
Y1 - 2007
N2 - Bacteriochlorophyll (BChl) c is the major photosynthetic pigment in the green sulfur bacterium Chlorobaculum tepidum, in which it forms protein-independent aggregates that function in light harvesting. BChls c, d, and e are found only in chlorosome-producing bacteria and are unique among chlorophylls because of methylations that occur at the C-8(2) and C-12(1) carbons. Two genes required for these methylation reactions were identified and designated bchQ (CT1777) and bchR (CT1320). BchQ and BchR are members of the radical S-adenosylmethionine (SAM) protein superfamily; each has sequence motifs to ligate a [4Fe-4S] cluster, and we propose that they catalyze the methyl group transfers. bchQ, bchR, and bchQ bchR mutants of C. tepidum were constructed and characterized. The bchQ mutant produced BChl c that was not methylated at C-8(2), the bchR mutant produced BChl c that was not methylated at C-12(1), and the double mutant produced [8-ethyl, 12-methyl]-BChl c that lacked methylation at both the C-8(2) and C-12(1) positions. Compared to the wild type, the Qy absorption bands for BChl c in the mutant cells were narrower and blue shifted to various extents. All three mutants grew slower and had a lower cellular BChl c content than the wild type, an effect that was especially pronounced at low light intensities. These observations show that the C-8(2) and C-12(1) methylations of BChl c play important roles in the adaptation of C. tepidum to low light intensity. The data additionally suggest that these methylations also directly or indirectly affect the regulation of the BChl c biosynthetic pathway.
AB - Bacteriochlorophyll (BChl) c is the major photosynthetic pigment in the green sulfur bacterium Chlorobaculum tepidum, in which it forms protein-independent aggregates that function in light harvesting. BChls c, d, and e are found only in chlorosome-producing bacteria and are unique among chlorophylls because of methylations that occur at the C-8(2) and C-12(1) carbons. Two genes required for these methylation reactions were identified and designated bchQ (CT1777) and bchR (CT1320). BchQ and BchR are members of the radical S-adenosylmethionine (SAM) protein superfamily; each has sequence motifs to ligate a [4Fe-4S] cluster, and we propose that they catalyze the methyl group transfers. bchQ, bchR, and bchQ bchR mutants of C. tepidum were constructed and characterized. The bchQ mutant produced BChl c that was not methylated at C-8(2), the bchR mutant produced BChl c that was not methylated at C-12(1), and the double mutant produced [8-ethyl, 12-methyl]-BChl c that lacked methylation at both the C-8(2) and C-12(1) positions. Compared to the wild type, the Qy absorption bands for BChl c in the mutant cells were narrower and blue shifted to various extents. All three mutants grew slower and had a lower cellular BChl c content than the wild type, an effect that was especially pronounced at low light intensities. These observations show that the C-8(2) and C-12(1) methylations of BChl c play important roles in the adaptation of C. tepidum to low light intensity. The data additionally suggest that these methylations also directly or indirectly affect the regulation of the BChl c biosynthetic pathway.
U2 - 10.1128/JB.00519-07
DO - 10.1128/JB.00519-07
M3 - Journal article
C2 - 17586634
SN - 0021-9193
VL - 189
SP - 6176
EP - 6184
JO - Journal of Bacteriology
JF - Journal of Bacteriology
IS - 17
ER -