2.A.85.2.3
The root aluminum-activated malate efflux transporter, ALMT1 (required for aluminum tolerance) (Hoekenga et al., 2006).  Also called Quick Anion Channel, QUAC, based on activation kinetics of anion channel currents in response to voltage changes.  Evolutionary studies have been reported (Dreyer et al. 2012).  Plants respond to aluminum (Al) ions by releasing malate from their root apices via ALMT1 with malate bound to the toxic Al ions, contributing to Al tolerance (Sasaki et al. 2014). ALMT1 mediates the efflux of malate to chelate the Al³⁺ in acidic soils and underlies the plant's Al resistance. Wang et al. 2021 presented cryo-EM structures of AtALMT1 in the apo, malate-bound, and Al-bound states at up to 3.0 Å resolution. The AtALMT1 dimer assembles an anion channel, and each subunit contains six transmembrane helices (TMSs) as well as six cytosolic α-helices. Two pairs of Arg residues are located in the center of the channel pore and contribute to malate recognition. Al binds at the extracellular side of AtALMT1 and induces conformational changes of the TMS 1-2 loop and the TMS 5-6 loop, resulting in the opening of the extracellular gate (Wang et al. 2021). Qin et al. 2022 provided insight into the gating and modulation of the ALMT12/QUAC1 anion channel in Glycine max (soybean). Picrotoxin inhibits anion flux but not GABA flux (Ramesh et al. 2022).