title: The phosphatidic acid binding site of the Arabidopsis trigalactosyldiacylglycerol 4 (TGD4) protein required for lipid import into chloroplasts.
abstract: Chloroplast membrane lipid synthesis relies on the import of glycerolipids from the ER. The TGD (TriGalactosylDiacylglycerol) proteins are required for this lipid transfer process. The TGD1, -2, and -3 proteins form a putative ABC (ATP-binding cassette) transporter transporting ER-derived lipids through the inner envelope membrane of the chloroplast, while TGD4 binds phosphatidic acid (PtdOH) and resides in the outer chloroplast envelope. We identified two sequences in TGD4, amino acids 1-80 and 110-145, which are necessary and sufficient for PtdOH binding. Deletion of both sequences abolished PtdOH binding activity. We also found that TGD4 from 18:3 plants bound specifically and with increased affinity PtdOH. TGD4 did not interact with other proteins and formed a homodimer both in vitro and in vivo. Our results suggest that TGD4 is an integral dimeric β-barrel lipid transfer protein that binds PtdOH with its N terminus and contains dimerization domains at its C terminus.
authors.affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Wang
authors.forename: Nicholas Scott
authors.initials: NS
authors.lastname: Anderson
authors.forename: Christoph
authors.initials: C
authors.lastname: Benning
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D002736:Chloroplasts / Q000378:metabolism*; D019281:Dimerization; D004721:Endoplasmic Reticulum / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D007425:Intracellular Membranes / Q000378:metabolism; D008055:Lipids / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry; D026901:Membrane Transport Proteins / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D010712:Phosphatidic Acids / Q000737:chemistry*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D029681:Arabidopsis Proteins; D008055:Lipids; D008081:Liposomes; D026901:Membrane Transport Proteins; D010712:Phosphatidic Acids; C534346:TGD4 protein, Arabidopsis