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Emerging Concepts in Ion Channel Biophysics
Thursday Speaker Abstracts
27
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.