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The crystal structure of Arabidopsis thaliana galactolipid synthase, MGD1 (apo-form)
Structural highlights
FunctionMGDG1_ARATH Involved in the synthesis of the major structural component of photosynthetic membranes. Required for proper thylakoid membrane biogenesis. Does not discriminate between prokaryotic (18:1/16:0) or eukaryotic (18:2/18:2) 1,2-diacylglycerol species, but operates with some preference for the prokaryotic one.[1] [2] [3] [4] Publication Abstract from PubMedMonogalactosyldiacylglycerol (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. Structural insights and membrane binding properties of MGD1, the major galactolipid synthase in plants.,Rocha J, Sarkis J, Thomas A, Pitou L, Radzimanowski J, Audry M, Chazalet V, de Sanctis D, Palcic MM, Block MA, Girard-Egrot A, Marechal E, Breton C Plant J. 2016 Mar;85(5):622-33. doi: 10.1111/tpj.13129. Epub 2016 Feb 23. PMID:26935252[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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