Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Thursday Speaker Abstracts

The Role of the Selectivity Filter in Gating of the TRPV1 Channel Andres Jara-Oseguera , Kenton J. Swartz. NINDS NIH, Bethesda, MD, USA.

The TRPV1 channel is a homotetrameric non-selective cation channel that functions in nociceptors as an integrator of external noxious stimuli and endogenous pro-inflammatory signaling molecules. Although the binding sites for some TRPV1 modulators have been characterized at the functional and structural level, we still don’t understand how any of these stimuli influence ion conduction in this receptor. The identification and functional characterization of the regions that function as activation gates are therefore central to understanding the mechanisms of opening and closing in the TRPV1 and other related channels. The cryo-EM structures of TRPV1 in open and closed states suggested that in addition to the intracellular gate formed by the pore-lining S6 helices, the selectivity filter could also function as an activation gate. Here we set out to determine whether the selectivity filter of TRPV1 functions as a gate, while also establishing tools to probe gating-associated conformational changes in the ion conduction pathway to investigate how this channel integrates signals from distinct modulators. We have substituted cysteines along the pore and assessed their accessibility to externally applied cadmium and silver ions in both the open and the closed states in patch clamp recordings. Our data so far suggests that the selectivity filter is not an activation gate. However, it is likely that high ion occupancy in the conduction pathway when the S6 helix gate is closed limits accessibility for external cations to cysteines located intracellularly relative to the filter. Even if the open/closed conformation of the filter does not depend on channel activation level, it is possible that the filter adopts a non-conducting conformation as observed in the structure under specific conditions yet to be identified, or that it constitutes a highly dynamic region of the receptor.

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