title: Subcellular localization of monoglucosyldiacylglycerol synthase in Synechocystis sp. PCC6803 and its unique regulation by lipid environment.
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.
authors: School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
authors: Tiago Toscano
authors: TT
authors: Selão
authors: School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
authors: Lifang
authors: L
authors: Zhang
authors: Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, Stockholm, Sweden.
authors: Candan
authors: C
authors: Ariöz
authors: Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, Stockholm, Sweden.
authors: Åke
authors: Å
authors: Wieslander
authors: School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
authors: Birgitta
authors: B
authors: Norling
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism*; D053898:Biosynthetic Pathways / Q000187:drug effects; D015153:Blotting, Western; D002247:Carbon Isotopes; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002855:Chromatography, Thin Layer; D017124:Conserved Sequence; D020536:Enzyme Activators / Q000494:pharmacology; D005964:Glucosyltransferases / Q000737:chemistry / Q000378:metabolism*; D006017:Glycolipids / Q000494:pharmacology; D008055:Lipids / Q000096:biosynthesis / Q000737:chemistry*; D008823:Micelles; D008954:Models, Biological; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D021381:Protein Transport / Q000187:drug effects; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000187:drug effects / Q000201:enzymology; D046939:Synechocystis / Q000187:drug effects / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D002247:Carbon Isotopes; D020536:Enzyme Activators; D006017:Glycolipids; D008055:Lipids; D008823:Micelles; C013694:sulfoquinovosyl diglyceride; D005964:Glucosyltransferases; C103660:1,2-diacylglycerol 3-glucosyltransferase