The Selectivity Filter of the TRPV1 Channel Does Not Function as an Activation Gate

Abstract

TRPV1 channels in nociceptors result in the sensation of pain when activated by noxious stimuli or inflammatory mediators. Such TRPV1 activators open the pore of the channel to enable calcium and sodium ions to permeate into the neuron. Pore opening has been proposed to involve two regions of TRPV1 that appear to occlude permeation in the absence of activation: the selectivity filter on the external side of the pore and the S6 helices that line the cytosolic half of the pore. Here we reveal that the selectivity filter of TRPV1 adopts a conformation that can conduct cations in the absence of activation, indicating that only the S6 helices control opening and closing of the pore. We find that the filter also does not function as an activation gate in the TRPV2 and TRPV3 channels, which share around 50% amino acid sequence identity in the pore domain with TRPV1 but are not sensitive to most stimuli that activate TRPV1, suggesting that the core gating mechanism is conserved between these channels despite their distinct agonist-sensitivities. Although the selectivity filter does not function as an activation gate, we find evidence that it undergoes conformational changes upon channel activation. We propose that these conformational changes function to couple agonist-elicited changes in the extracellular side of the pore to the opening of the cytosolic activation gate.