Conserved Gating Elements in TRPC4 and TRPC5 Channels

TRPC4 and TRPC5 proteins share 65% amino acid sequence identity and form Ca2+ -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 Ca2+ of the culture medium. Current- voltage relationships of the TRPC4G(503S) 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.