title: C-terminus-mediated voltage gating of Arabidopsis guard cell anion channel QUAC1.
abstract: Anion transporters in plants play a fundamental role in volume regulation and signaling. Currently, two plasma membrane-located anion channel families—SLAC/SLAH and ALMT—are known. Among the ALMT family, the root-expressed ALuminium-activated Malate Transporter 1 was identified by comparison of aluminum-tolerant and Al(3+)-sensitive wheat cultivars and was subsequently shown to mediate voltage-independent malate currents. In contrast, ALMT12/QUAC1 (QUickly activating Anion Channel1) is expressed in guard cells transporting malate in an Al(3+)-insensitive and highly voltage-dependent manner. So far, no information is available about the structure and mechanism of voltage-dependent gating with the QUAC1 channel protein. Here, we analyzed gating of QUAC1-type currents in the plasma membrane of guard cells and QUAC1-expressing oocytes revealing similar voltage dependencies and activation–deactivation kinetics. In the heterologous expression system, QUAC1 was electrophysiologically characterized at increasing extra- and intracellular malate concentrations. Thereby, malate additively stimulated the voltage-dependent QUAC1 activity. In search of structural determinants of the gating process, we could not identify transmembrane domains common for voltage-sensitive channels. However, site-directed mutations and deletions at the C-terminus of QUAC1 resulted in altered voltage-dependent channel activity. Interestingly, the replacement of a single glutamate residue, which is conserved in ALMT channels from different clades, by an alanine disrupted QUAC1 activity. Together with C- and N-terminal tagging, these results indicate that the cytosolic C-terminus is involved in the voltage-dependent gating mechanism of QUAC1.
authors: Institute for Molecular Plant Physiology and Biophysics, University of Würzburg, Julius-von-Sachs Platz 2, D-97082 Würzburg, Germany.
authors: Patrick
authors: P
authors: Mumm
authors: Dennis
authors: D
authors: Imes
authors: Enrico
authors: E
authors: Martinoia
authors: Khaled A S
authors: KA
authors: Al-Rasheid
authors: Dietmar
authors: D
authors: Geiger
authors: Irene
authors: I
authors: Marten
authors: Rainer
authors: R
authors: Hedrich
mesh_terms: D000818:Animals; D017360:Arabidopsis / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D005453:Fluorescence; D018698:Glutamic Acid / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects; D007473:Ion Channels / Q000737:chemistry / Q000378:metabolism*; D008293:Malates / Q000494:pharmacology; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D009928:Organ Specificity / Q000187:drug effects; D027361:Organic Anion Transporters / Q000737:chemistry / Q000378:metabolism*; D054046:Plant Stomata / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
chemical_list: D029681:Arabidopsis Proteins; D007473:Ion Channels; D008293:Malates; D050505:Mutant Proteins; D027361:Organic Anion Transporters; C587314:QUAC1 protein, Arabidopsis; D011993:Recombinant Fusion Proteins; D018698:Glutamic Acid; C030298:malic acid
keywords: C-terminal deactivation; R-type/QUAC-type anion channel; gating modifier.; single-channel conductance