Molecular Bases of Multimodal Regulation of a Fungal Transient Receptor Potential (TRP) Channel

Multimodal activation by various stimuli is a fundamental characteristic of TRP channels. Weidentified a fungal TRP channel, TRPGz, exhibiting activation by hyperosmolarity, temperatureincrease, cytosolic Ca²⁺ elevation, membrane potential, andH₂O₂ application, and thus it is expected to represent a prototypic multimodalTRP channel. TRPGz possesses a cytosolic C-terminal domain (CTD), primarily composed ofintrinsically disordered regions with some regulatory modules, a putative coiled-coil region and abasic residue cluster. The CTD oligomerization mediated by the coiled-coil region is required forthe hyperosmotic and temperature increase activations but not for the tetrameric channel formationor other activation modalities. In contrast, the basic cluster is responsible for general channelinhibition, by binding to phosphatidylinositol phosphates. The crystal structure of the presumedcoiled-coil region revealed a tetrameric assembly in an offset spiral rather than a canonicalcoiled-coil. This structure underlies the observed moderate oligomerization affinity enabling thedynamic assembly and disassembly of the CTD during channel functions, which are compatible with themultimodal regulation mediated by each functional module.