Conserved Gating Elements in TRPC4 and TRPC5 Channels

Abstract

TRPC4 and TRPC5 proteins share 65% amino acid sequence identity and form Ca 2+ -permeable nonselective cation channels. They are activated by stimulation of receptors coupled to the phosphoinositide signaling cascade. Replacing a conserved glycine residue within the cytosolic S4–S5 linker of both proteins by a serine residue forces the channels into an open conformation. Expression of the TRPC4 G503S and TRPC5 G504S mutants causes cell death, which could be prevented by buffering the Ca 2+ of the culture medium. Current-voltage relationships of the TRPC4 G503S and TRPC5 G504S mutant ion channels resemble that of fully activated TRPC4 and TRPC5 wild-type channels, respectively. Modeling the structure of the transmembrane domains and the pore region (S4-S6) of TRPC4 predicts a conserved serine residue within the C-terminal sequence of the predicted S6 helix as a potential interaction site. Introduction of a second mutation (S623A) into TRPC4 G503S suppressed the constitutive activation and partially rescued its function. These results indicate that the S4–S5 linker is a critical constituent of TRPC4/C5 channel gating and that disturbance of its sequence allows channel opening independent of any sensor domain. Background: Gating mechanisms of TRPC channels are mostly unknown. Results: Replacing the highly conserved glycine residue within the linker between transmembrane domains 4 and 5 by serine renders TRPC4 and TRPC5 channels constitutively active. Conclusion: TRPC channel opening seems to require similar constraints than the voltage-gated potassium channels. Significance: Novel mechanistic insights into structural requirements of TRPC channel gating are provided.