title: Structural insights and membrane binding properties of MGD1, the major galactolipid synthase in plants.
abstract: Monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) are the major lipid components of photosynthetic membranes, and hence the most abundant lipids in the biosphere. They are essential for assembly and function of the photosynthetic apparatus. In Arabidopsis, the first step of galactolipid synthesis is catalyzed by MGDG synthase 1 (MGD1), which transfers a galactosyl residue from UDP-galactose to diacylglycerol (DAG). MGD1 is a monotopic protein that is embedded in the inner envelope membrane of chloroplasts. Once produced, MGDG is transferred to the outer envelope membrane, where DGDG synthesis occurs, and to thylakoids. Here we present two crystal structures of MGD1: one unliganded and one complexed with UDP. MGD1 has a long and flexible region (approximately 50 amino acids) that is required for DAG binding. The structures reveal critical features of the MGD1 catalytic mechanism and its membrane binding mode, tested on biomimetic Langmuir monolayers, giving insights into chloroplast membrane biogenesis. The structural plasticity of MGD1, ensuring very rapid capture and utilization of DAG, and its interaction with anionic lipids, possibly driving the construction of lipoproteic clusters, are consistent with the role of this enzyme, not only in expansion of the inner envelope membrane, but also in supplying MGDG to the outer envelope and nascent thylakoid membranes.
authors.affiliation: University of Grenoble Alpes, 38400, Grenoble, France.|Centre National de la Recherche Scientifique/Centre de Recherches sur les Macromolécules Végétales, 38041, Grenoble, France.
authors.forename: Joana
authors.initials: J
authors.lastname: Rocha
authors.affiliation: GEMBAS Team, Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, UMR 5246, University of Lyon, 69622, Villeurbanne, France.
authors.forename: Joe
authors.initials: J
authors.lastname: Sarkis
authors.affiliation: University of Grenoble Alpes, 38400, Grenoble, France.|Centre National de la Recherche Scientifique/Centre de Recherches sur les Macromolécules Végétales, 38041, Grenoble, France.
authors.forename: Aline
authors.initials: A
authors.lastname: Thomas
authors.affiliation: University of Grenoble Alpes, 38400, Grenoble, France.|Centre National de la Recherche Scientifique/Centre de Recherches sur les Macromolécules Végétales, 38041, Grenoble, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Pitou
authors.affiliation: University of Grenoble Alpes, 38400, Grenoble, France.|Unit of Virus Host-Cell Interactions, University Joseph Fourier/European Molecular Biology Laboratory/Centre National de la Recherche Scientifique, 38000, Grenoble, France.
authors.forename: Jens
authors.initials: J
authors.lastname: Radzimanowski
authors.affiliation: University of Grenoble Alpes, 38400, Grenoble, France.|Centre National de la Recherche Scientifique/Centre de Recherches sur les Macromolécules Végétales, 38041, Grenoble, France.
authors.forename: Magali
authors.initials: M
authors.lastname: Audry
authors.affiliation: University of Grenoble Alpes, 38400, Grenoble, France.|Centre National de la Recherche Scientifique/Centre de Recherches sur les Macromolécules Végétales, 38041, Grenoble, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Chazalet
authors.affiliation: European Synchrotron Radiation Facility, 38000, Grenoble, France.
authors.forename: Daniele
authors.initials: D
authors.lastname: de Sanctis
authors.affiliation: Carlsberg Laboratory, Gamle Carlsberg Vej 10, 1799, Copenhagen V, Denmark.
authors.forename: Monica M
authors.initials: MM
authors.lastname: Palcic
authors.affiliation: University of Grenoble Alpes, 38400, Grenoble, France.|Laboratoire Physiologie Cellulaire & Végétale, UMR 5168, CEA Grenoble, 38054, Grenoble, France.
authors.forename: Maryse A
authors.initials: MA
authors.lastname: Block
authors.affiliation: GEMBAS Team, Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, UMR 5246, University of Lyon, 69622, Villeurbanne, France.
authors.forename: Agnès
authors.initials: A
authors.lastname: Girard-Egrot
authors.affiliation: University of Grenoble Alpes, 38400, Grenoble, France.|Laboratoire Physiologie Cellulaire & Végétale, UMR 5168, CEA Grenoble, 38054, Grenoble, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Maréchal
authors.affiliation: University of Grenoble Alpes, 38400, Grenoble, France.|Centre National de la Recherche Scientifique/Centre de Recherches sur les Macromolécules Végétales, 38041, Grenoble, France.
authors.forename: Christelle
authors.initials: C
authors.lastname: Breton
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D055162:Biocatalysis; D053898:Biosynthetic Pathways / Q000235:genetics; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004075:Diglycerides / Q000737:chemistry / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D038983:Galactolipids / Q000096:biosynthesis*; D005690:Galactose / Q000737:chemistry / Q000378:metabolism; D005700:Galactosyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D000072417:Protein Domains; D017433:Protein Structure, Secondary; D053838:Scattering, Small Angle; D017386:Sequence Homology, Amino Acid; D020524:Thylakoids / Q000378:metabolism*; D014530:Uridine Diphosphate / Q000737:chemistry / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D029681:Arabidopsis Proteins; D004075:Diglycerides; D038983:Galactolipids; C007388:digalactosyldiacylglycerol; C009909:monogalactosyldiacylglycerol; D014530:Uridine Diphosphate; D005700:Galactosyltransferases; C528622:MGD1 protein, Arabidopsis; D005690:Galactose
keywords: Arabidopsis; At4g31780; MGD1; MGDG; chloroplast; crystal structure; galactolipids