The cluster of acidic residues in the C terminus of TRPA1 contributes to calcium sensing

Lucie Surá, Lenka Maršáková, Anna Hynková, Viktorie Vlachová

Department of Cellular Neurophysiology, Institute of Physiology, Academy of Sciences of the Czech Republic, Videnska 1083, 142 20 Prague 4, Czech Republic

The ankyrin transient receptor potential channel TRPA1 is a Ca²⁺-permeable, voltage-sensing cation channel. It is predominantly expressed in a subpopulation of nociceptive neurons. There it mainly acts as a polymodal sensor, activated by pungent compounds. From the cytoplasmic side, TRPA1 is critically regulated by Ca²⁺ ions and this mechanism represents a self-modulating feedback loop that either augments or inhibits the initial activation. It has been suggested that an EF-hand like domain in the N-terminus is responsible for Ca²⁺ dependent activation, but these results have been questioned. Here, we suggested for such role the cluster of acidic residues in the distal C-terminus. We investigated its contribution to Ca²⁺ sensing using mutagenesis and whole-cell electrophysiology. We found that neutralization of four conserved residues, namely Glu1077 and Asp1080-Asp1082 in human TRPA1, had strong effects on Ca²⁺- and voltage-dependent potentiation and/or inactivation of agonist-induced responses. In addition, the surprising finding of this study was that truncation of the C-terminus by only 20 residues selectively slowed down the Ca²⁺-dependent inactivation by 2.9-fold without affecting other functional parameters. Our findings identify the conserved acidic motif in the C-terminus that is actively involved in TRPA1 channel modulation by Ca²⁺ and may represent its long-sought Ca²⁺-sensing domain.