title: Substrate specificity and expression profile of amino acid transporters (AAPs) in Arabidopsis.
abstract: Three amino acid transporter genes (AAP3-5) were isolated from Arabidopsis by complementation of a yeast mutant defective in histidine uptake. Transport is driven against a concentration gradient and sensitive to protonophores. Analysis of the substrate specificity demonstrates that the carriers have a broad substrate specificity covering the major transport forms of reduced nitrogen, i.e. glutamine and glutamate. The transporters have similar affinities for glutamate, glutamine, and alanine but differ with respect to valine, phenylalanine, histidine, arginine, and lysine. AAP3 and AAP5 efficiently transport arginine and lysine and are involved in basic amino acid transport. The predicted polypeptides of 53 kDa are highly hydrophobic with 12 putative membrane-spanning regions and show significant homologies to Arabidopsis amino acid transporters AAP1 and AAP2. Each of the genes has a different organ-specific expression in the plant. AAP3 is exclusively expressed in roots and AAP4 mainly in source leaves, stems, and flowers, whereas AAP5 is found in all tissues. The specific distribution in the plant and the different substrate specificities of AAP transporters may indicate that tissues differ both qualitatively and quantitatively regarding import or export of amino acids.
authors.affiliation: Institut für Genbiologische Forschung, Berlin, Germany.
authors.forename: W N
authors.initials: WN
authors.lastname: Fischer
authors.forename: M
authors.initials: M
authors.lastname: Kwart
authors.forename: S
authors.initials: S
authors.lastname: Hummel
authors.forename: W B
authors.initials: WB
authors.lastname: Frommer
mesh_terms: D000595:Amino Acid Sequence; D026905:Amino Acid Transport Systems; D000596:Amino Acids / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active / Q000235:genetics; D015139:Blotting, Southern; D015870:Gene Expression; D005816:Genetic Complementation Test; D018745:Genome, Plant; D006863:Hydrogen-Ion Concentration; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000378:metabolism*; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014018:Tissue Distribution
chemical_list: D026905:Amino Acid Transport Systems; D000596:Amino Acids; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D011994:Recombinant Proteins