Structure of the voltage-gated two-pore channel TPC1 from Arabidopsis thaliana

Abstract

Two-pore channels (TPCs) contain two copies of a Shaker-like six-transmembrane (6-TM) domain in each subunit and are ubiquitously expressed in both animals and plants as organellar cation channels. Here, we present the first crystal structure of a vacuolar two-pore channel from Arabidopsis thaliana, AtTPC1, which functions as a homodimer. AtTPC1 activation requires both voltage and cytosolic Ca2+. Ca2+ binding to the cytosolic EF-hand domain triggers conformational changes coupled to the pair of pore-lining inner helices (IS6 helices) from the first 6-TM domains, whereas membrane potential only activates the second voltage-sensing domain (VSD2) whose conformational changes are coupled to the pair of inner helices (IIS6 helices) from the second 6-TM domains. Luminal Ca2+ or Ba2+ can modulate voltage activation by stabilizing VSD2 in the resting state and shifts voltage activation towards more positive potentials. Our Ba2+ bound AtTPC1 structure reveals a voltage sensor in the resting state, providing hitherto unseen structural insight into the general voltage-gating mechanism among voltage-gated channels.

Interplay of Plasma Membrane and Vacuolar Ion Channels, Together with BAK1, Elicits Rapid Cytosolic Calcium Elevations in Arabidopsis during Aphid Feeding

“…Since the feeding site [Ca 2+ ] cyt elevations are attenuated, but not abolished in the tpc1-2 mutant, it appears that release of vacuolar Ca 2+ by TPC1 is downstream of and dependent on extracellular Ca 2+ release by the GLRs. This finding agrees with work showing that TPC1 activity is positively regulated by [Ca 2+ ] cyt (Hedrich and Neher, 1987;Ward and Schroeder, 1994;Allen and Sanders, 1996;Guo et al, 2016;Kintzer and Stroud, 2016) and plays a role in systemically propagating Ca 2+ -induced Ca 2+ release (Dubiella et al, 2013;Evans et al, 2016;Gilroy et al, 2016;Choi et al, 2016). Consequently, TPC1 appears to be activated by GLR-mediated Ca 2+ influx and involved in the cell-to-cell spread of Ca 2+ during biotic interactions.…”

“…In addition, herbivory-elicited Ca 2+ signals are attenuated in null mutants of the vacuolar channel TWO-PORE CHANNEL1 (TPC1) (Kiep et al, 2015). TPC1 is a tonoplast-localized Ca 2+ -permeable channel whose activity is regulated by voltage and Ca 2+ (Hedrich and Neher, 1987;Ward and Schroeder, 1994;Peiter et al, 2005;Gradogna et al, 2009;Guo et al, 2016Guo et al, , 2017Kintzer and Stroud, 2016). TPC1 also has an established role in systemic Ca 2+ signaling in response to salt stress (Choi et al, 2014;Evans et al, 2016) and wounding (Kiep et al, 2015) via its positive regulation by Ca 2+ in a process termed Ca 2+ -induced Ca 2+ release.…”

Structures of the calcium-activated, non-selective cation channel TRPM4

“…10b). Furthermore, the S4 helix runs antiparallel to the S5 helix of a neighboring subunit with extensive hydrophobic interactions and is unlikely to undergo a similar translational movement expected for a voltage-sensing S4 38–40 (Fig. 4a).…”

ROS, Calcium, and Electric Signals: Key Mediators of Rapid Systemic Signaling in Plants

“…Thus, propagation of NaCl-and wound-induced Ca 2+ waves are dependent on the slow vacuolar ion channel encoded by TPC1 (Choi et al, 2014;Kiep et al, 2015). Mutation in the vacuolar Ca 2+ -sensing domain of this channel (Beyhl et al, 2009;Dadacz-Narloch et al, 2011;Guo et al, 2016) also leads to up-regulation of jasmonate production, a hormone intimately linked to systemic wound responses (e.g. Bonaventure et al, 2007), reinforcing the idea that the regulation of this channel might be linked to these kinds of systemic response systems.…”