title: A small ATPase protein of Arabidopsis, TGD3, involved in chloroplast lipid import.
abstract: Polar lipid trafficking is essential in eukaryotic cells as membranes of lipid assembly are often distinct from final destination membranes. A striking example is the biogenesis of the photosynthetic membranes (thylakoids) in plastids of plants. Lipid biosynthetic enzymes at the endoplasmic reticulum and the inner and outer plastid envelope membranes are involved. This compartmentalization requires extensive lipid trafficking. Mutants of Arabidopsis are available that are disrupted in the incorporation of endoplasmic reticulum-derived lipid precursors into thylakoid lipids. Two proteins affected in two of these mutants, trigalactosyldiacylglycerol 1 (TGD1) and TGD2, encode the permease and substrate binding component, respectively, of a proposed lipid translocator at the inner chloroplast envelope membrane. Here we describe a third protein of Arabidopsis, TGD3, a small ATPase proposed to be part of this translocator. As in the tgd1 and tgd2 mutants, triacylglycerols and trigalactolipids accumulate in a tgd3 mutant carrying a T-DNA insertion just 5' of the TGD3 coding region. The TGD3 protein shows basal ATPase activity and is localized inside the chloroplast beyond the inner chloroplast envelope membrane. Proteins orthologous to TGD1, -2, and -3 are predicted to be present in Gram- bacteria, and the respective genes are organized in operons suggesting a common biochemical role for the gene products. Based on the current analysis, it is hypothesized that TGD3 is the missing ATPase component of a lipid transporter involving TGD1 and TGD2 required for the biosynthesis of ER-derived thylakoid lipids in Arabidopsis.
authors.affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, 48824-1312, USA.
authors.forename: Binbin
authors.initials: B
authors.lastname: Lu
authors.forename: Changcheng
authors.initials: C
authors.lastname: Xu
authors.forename: Koichiro
authors.initials: K
authors.lastname: Awai
authors.forename: A Daniel
authors.initials: AD
authors.lastname: Jones
authors.forename: Christoph
authors.initials: C
authors.lastname: Benning
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D052179:Antigens, Plant / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D006090:Gram-Negative Bacteria / Q000201:enzymology / Q000235:genetics; D007425:Intracellular Membranes / Q000201:enzymology; D050356:Lipid Metabolism / Q000502:physiology*; D008055:Lipids; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009876:Operon / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D020524:Thylakoids / Q000201:enzymology* / Q000235:genetics
chemical_list: D052179:Antigens, Plant; D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D008055:Lipids; D026901:Membrane Transport Proteins; D010940:Plant Proteins; C475468:TGD1 protein, Arabidopsis; C512987:TGD2 protein, Arabidopsis; C511920:lipid transfer proteins, plant; D000251:Adenosine Triphosphatases; C525795:TGD3 protein, Arabidopsis