Comparative genomic analysis revealed a gene for monoglucosyldiacylglycerol synthase, an enzyme for photosynthetic membrane lipid synthesis in cyanobacteria

Graduate School for Bioscience and Biotechnology , Tokyo Institute of Technology, Yokohama 226-8501, Japan.
Plant physiology (Impact Factor: 6.84). 08/2006; 141(3):1120-7. DOI: 10.1104/pp.106.082859
Source: PubMed


Cyanobacteria have a thylakoid lipid composition very similar to that of plant chloroplasts, yet cyanobacteria are proposed to synthesize monogalactosyldiacylglycerol (MGDG), a major membrane polar lipid in photosynthetic membranes, by a different pathway. In addition, plant MGDG synthase has been cloned, but no ortholog has been reported in cyanobacterial genomes. We report here identification of the gene for monoglucosyldiacylglycerol (MGlcDG) synthase, which catalyzes the first step of galactolipid synthesis in cyanobacteria. Using comparative genomic analysis, candidates for the gene were selected based on the criteria that the enzyme activity is conserved between two species of cyanobacteria (unicellular [Synechocystis sp. PCC 6803] and filamentous [Anabaena sp. PCC 7120]), and we assumed three characteristics of the enzyme; namely, it harbors a glycosyltransferase motif, falls into a category of genes with unknown function, and shares significant similarity in amino acid sequence between these two cyanobacteria. By a motif search of all genes of Synechocystis, BLAST searches, and similarity searches between these two cyanobacteria, we identified four candidates for the enzyme that have all the characteristics we predicted. When expressed in Escherichia coli, one of the Synechocystis candidate proteins showed MGlcDG synthase activity in a UDP-glucose-dependent manner. The ortholog in Anabaena also showed the same activity. The enzyme was predicted to require a divalent cation for its activity, and this was confirmed by biochemical analysis. The MGlcDG synthase and the plant MGDG synthase shared low similarity, supporting the presumption that cyanobacteria and plants utilize different pathways to synthesize MGDG.

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Available from: Yuki Nakamura, May 04, 2015
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    • "It is important to note that in cyanobacteria, MGDG is not synthesized by a homolog of MGDG synthases, but after a two-step process [127]. In cyanobacteria, MGlcDG is synthesized by transfer of a glucosyl residue from a UDP-Glc donor to a DAG acceptor [128]. The glucosyl "
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    ABSTRACT: Glycerolipids constituting the matrix of photosynthetic membranes, from cyanobacteria to chloroplasts of eukaryotic cells, comprise monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol and phosphatidylglycerol. This review covers our current knowledge on the structural and functional features of these lipids in various cellular models, from prokaryotes to eukaryotes. Their relative proportions in thylakoid membranes result from highly regulated and compartmentalized metabolic pathways, with a cooperation, in the case of eukaryotes, of non plastidic compartments. This review also focuses on the role of each of these thylakoid glycerolipids in stabilizing protein complexes of the photosynthetic machinery, which might be one of the reasons for their fascinating conservation in the course of evolution. This article is part of a Special Issue entitled: Dynamic and ultrastructure of bioenergetic membranes and their components.
    Biochimica et Biophysica Acta 04/2014; 1837(4):470-480. DOI:10.1016/j.bbabio.2013.09.007 · 4.66 Impact Factor
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    • "First, an as yet unknown MGS-type enzyme located exclusively in the TM, may be responsible for the high activity observed there. As previously mentioned, deletion of the sll1377 gene is lethal to Synechocystis [15] so such an enzyme, if it exists is unable to compensate for the loss of MgdA under these circumstances. "
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    ABSTRACT: Synthesis of monogalactosyldiacylglycerol (GalDAG) and digalactosyldiacylglycerol (GalGalDAG), the major membrane lipids in cyanobacteria, begins with production of the intermediate precursor monoglucosyldiacylglycerol (GlcDAG), by monoglucosyldiacylglycerol synthase (MGS). In Synechocystis sp. PCC6803 (Synechocystis) this activity is catalyzed by an integral membrane protein, Sll1377 or MgdA. In silico sequence analysis revealed that cyanobacterial homologues of MgdA are highly conserved and comprise a distinct group of lipid glycosyltransferases. Global regulation of lipid synthesis in Synechocystis and, more specifically, the influence of the lipid environment on MgdA activity have not yet been fully elucidated. Therefore, we purified membrane subfractions from this organism and assayed MGS activity in vitro, with and without different lipids and other potential effectors. Sulfoquinovosyldiacylglycerol (SQDAG) potently stimulates MgdA activity, in contrast to other enzymes of a similar nature, which are activated by phosphatidylglycerol instead. Moreover, the final products of galactolipid synthesis, GalDAG and GalGalDAG, inhibited this activity. Western blotting revealed the presence of MgdA both in plasma and thylakoid membranes, with a high specific level of the MgdA protein in the plasma membrane but highest MGS activity in the thylakoid membrane. This discrepancy in the subcellular localization of enzyme activity and protein may indicate the presence of either an unknown regulator and/or an as yet unidentified MGS-type enzyme. Furthermore, the stimulation of MgdA activity by SQDAG observed here provides a new insight into regulation of the biogenesis of both sulfolipids and galactolipids in cyanobacteria.
    PLoS ONE 02/2014; 9(2):e88153. DOI:10.1371/journal.pone.0088153 · 3.23 Impact Factor
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    • "In contrast, cyanobacteria must first synthesize monoglucosyl-DAG (MGlcDG) using UDP glucose (UDP-Glc) and DAG, which is subsequently epimerized to produce MGDG. In addition, sequence comparison indicates that MGDG synthase (MGD) genes belong to the glycosyltransferase 28 (GT28) family, whereas MGlcDG synthase (MGlcD) genes belong to the family GT2 [according to the Carbohydrate-Active Enzymes database (].11–13 In Viridiplantae (green algae and land plants), therefore, the precise origin of the pathway for MGDG synthesis is not clear. "
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    ABSTRACT: The photosynthetic membranes of cyanobacteria and chloroplasts of higher plants have remarkably similar lipid compositions. In particular, thylakoid membranes of both cyanobacteria and chloroplasts are composed of galactolipids, of which monogalactosyldiacylglycerol (MGDG) is the most abundant, although MGDG biosynthetic pathways are different in these organisms. Comprehensive phylogenetic analysis revealed that MGDG synthase (MGD) homologs of filamentous anoxygenic phototrophs Chloroflexi have a close relationship with MGDs of Viridiplantae (green algae and land plants). Furthermore, analyses for the sugar specificity and anomeric configuration of the sugar head groups revealed that one of the MGD homologs exhibited a true MGDG synthetic activity. We therefore presumed that higher plant MGDs are derived from this ancestral type of MGD genes, and genes involved in membrane biogenesis and photosystems have been already functionally associated at least at the time of Chloroflexi divergence. As MGD gene duplication is an important event during plastid evolution, we also estimated the divergence time of type A and B MGDs. Our analysis indicated that these genes diverged -323 million years ago, when Spermatophyta (seed plants) were appearing. Galactolipid synthesis is required to produce photosynthetic membranes; based on MGD gene sequences and activities, we have proposed a novel evolutionary model that has increased our understanding of photosynthesis evolution.
    DNA Research 12/2011; 19(1):91-102. DOI:10.1093/dnares/dsr044 · 5.48 Impact Factor
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