title: Fluorescent sensors reporting the activity of ammonium transceptors in live cells.
abstract: Ammonium serves as key nitrogen source and metabolic intermediate, yet excess causes toxicity. Ammonium uptake is mediated by ammonium transporters, whose regulation is poorly understood. While transport can easily be characterized in heterologous systems, measuring transporter activity in vivo remains challenging. Here we developed a simple assay for monitoring activity in vivo by inserting circularly-permutated GFP into conformation-sensitive positions of two plant and one yeast ammonium transceptors ('AmTrac' and 'MepTrac'). Addition of ammonium to yeast cells expressing the sensors triggered concentration-dependent fluorescence intensity (FI) changes that strictly correlated with the activity of the transporter. Fluorescence-based activity sensors present a novel technology for monitoring the interaction of the transporters with their substrates, the activity of transporters and their regulation in vivo, which is particularly valuable in the context of analytes for which no radiotracers exist, as well as for cell-specific and subcellular transport processes that are otherwise difficult to track. DOI:http://dx.doi.org/10.7554/eLife.00800.001.
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, United States.|Institute of Plant Genetics, Italian National Research Council (CNR-IGV), Palermo, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: De Michele
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, United States.|NanoPolyPhotonik, Fraunhofer Institute for Applied Polymer Research, Potsdam-Golm, Germany.
authors.forename: Cindy
authors.initials: C
authors.lastname: Ast
authors.affiliation: Feedstocks Division, Joint BioEnergy Institute, Emeryville, United States.
authors.forename: Dominique
authors.initials: D
authors.lastname: Loqué
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, United States.
authors.forename: Cheng-Hsun
authors.initials: CH
authors.lastname: Ho
authors.affiliation: Department of Biochemistry, Institute for Organic Chemistry and Biochemistry, and BIOSS Center for Biological Signalling Studies, University of Freiburg, Freiburg, Germany.
authors.forename: Susana LA
authors.initials: S
authors.lastname: Andrade
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, United States.
authors.forename: Viviane
authors.initials: V
authors.lastname: Lanquar
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, United States.
authors.forename: Guido
authors.initials: G
authors.lastname: Grossmann
authors.affiliation: Department of Physical Chemistry, Institute of Chemistry, University of Potsdam, Potsdam, Germany.
authors.forename: Sören
authors.initials: S
authors.lastname: Gehne
authors.affiliation: Department of Physical Chemistry, Institute of Chemistry, University of Potsdam, Potsdam, Germany.
authors.forename: Michael U
authors.initials: MU
authors.lastname: Kumke
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, United States.
authors.forename: Wolf B
authors.initials: WB
authors.lastname: Frommer
mesh_terms: D000595:Amino Acid Sequence; D064751:Ammonium Compounds / Q000378:metabolism*; D001483:Base Sequence; D015374:Biosensing Techniques; D004247:DNA; D005456:Fluorescent Dyes / Q000737:chemistry*; D049452:Green Fluorescent Proteins / Q000235:genetics; D007700:Kinetics; D008969:Molecular Sequence Data; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D064751:Ammonium Compounds; D005456:Fluorescent Dyes; D011956:Receptors, Cell Surface; D049452:Green Fluorescent Proteins; D004247:DNA
keywords: Arabidopsis; GFP; ammonium; biosensor; conformation; fluorescent probes; transport