title: TGD1, -2, and -3 proteins involved in lipid trafficking form ATP-binding cassette (ABC) transporter with multiple substrate-binding proteins.
abstract: Members of the ATP-binding cassette (ABC) transporter family are essential proteins in species as diverse as archaea and humans. Their domain architecture has remained relatively fixed across these species, with rare exceptions. Here, we show one exception to be the trigalactosyldiacylglycerol 1, 2, and 3 (TGD1, -2, and -3) putative lipid transporter located at the chloroplast inner envelope membrane. TGD2 was previously shown to be in a complex of >500 kDa. We demonstrate that this complex also contains TGD1 and -3 and is very stable because it cannot be broken down by gentle denaturants to form a "core" complex similar in size to standard ABC transporters. The complex was purified from Pisum sativum (pea) chloroplast envelopes by native gel electrophoresis and examined by mass spectrometry. Identified proteins besides TGD1, -2, or -3 included a potassium efflux antiporter and a TIM17/22/23 family protein, but these were shown to be in separate high molecular mass complexes. Quantification of the complex components explained the size of the complex because 8-12 copies of the substrate-binding protein (TGD2) were found per functional transporter.
authors.affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Roston
authors.forename: Jinpeng
authors.initials: J
authors.lastname: Gao
authors.forename: Monika W
authors.initials: MW
authors.lastname: Murcha
authors.forename: James
authors.initials: J
authors.lastname: Whelan
authors.forename: Christoph
authors.initials: C
authors.lastname: Benning
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D060365:Chloroplast Proteins / Q000235:genetics / Q000378:metabolism*; D050356:Lipid Metabolism / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D018532:Pisum sativum / Q000235:genetics / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D060365:Chloroplast Proteins; D026901:Membrane Transport Proteins; D046912:Multiprotein Complexes; C475468:TGD1 protein, Arabidopsis; C512987:TGD2 protein, Arabidopsis; D000251:Adenosine Triphosphatases; C525795:TGD3 protein, Arabidopsis