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C-Terminus-Mediated Voltage Gating of Arabidopsis Guard Cell Anion Channel QUAC1

Molecular Plant 2013年第5期6卷 1550-1563页

作者： Patrick Mumm dennis imes Enrico Martinoia Khaled A.S. AI-Rasheid Dietmar Geiger Irene Marten Rainer Hedrich Institute for Molecular Plant Physiology and Biophysics University of Wurzburg Julius-von-Sachs Platz 2 D-97082 Wurzburg Germany Institute of Plant Biology University of Zurich Zollikerstrasse 107 Zurich Switzerland King Saud University Zoology Department College of Science PO Box 2455 Riyadh 11451 Saudi Arabia

Anion transporters in plants play a fundamental role in volume regulation and signaling. Currently, two plasma membrane-located anion channel familiesmSLAC/SLAH and ALMTmare known. Among the ALMT family, the root-expressed ALuminium-activated Malate Transporter 1 was identified by comparison of aluminum-tolerant and Al3＋-sensitive wheat cultivars and was subsequently shown to mediate voltage-independent malate currents. In con- trast, ALMT12/QUAC1 （QUickly activating Anion Channel1） is expressed in guard cells transporting malate in an Al3＋- 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 QUACl-type currents in the plasma membrane of guard cells and QUACl-expressing oocytes revealing similar voltage dependencies and activation- deactivation kinetics. In the heterologous expression system, QUAC1 was electrophysiologically characterized at increas- ing 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 com- mon 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 con- served 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.

关键词： C-terminal deactivation R-type/QUAC-type anion channel single-channel conductance gating modifier.

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