title: Bacteriochlorophyllide c C-8(2) and C-12(1) methyltransferases are essential for adaptation to low light in Chlorobaculum tepidum.
abstract: 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.
authors.affiliation: Department of Biochemistry and Molecular Biology, S-235 Frear Building, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Aline
authors.initials: A
authors.lastname: Gomez Maqueo Chew
authors.forename: Niels-Ulrik
authors.initials: NU
authors.lastname: Frigaard
authors.forename: Donald A
authors.initials: DA
authors.lastname: Bryant
mesh_terms: D000222:Adaptation, Physiological; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001429:Bacteriochlorophylls / Q000737:chemistry / Q000378:metabolism*; D019414:Chlorobi / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D002735:Chlorophyllides / Q000378:metabolism*; D003593:Cytoplasm / Q000737:chemistry; D017353:Gene Deletion; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D016254:Mutagenesis, Insertional; D015388:Organelles / Q000648:ultrastructure; D013057:Spectrum Analysis
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D002735:Chlorophyllides; C002084:bacteriochlorophyll c; D008780:Methyltransferases