Mechanism of lipid-dependent cold sensitivity in a model ion channel.

Temperature sensing enables organisms to detect and respond to environmental changes. While temperature-responsive ion channels are key to this process, the physico-chemical mechanisms by which they sense temperature remain poorly understood. Here, we investigate the molecular details of temperature sensing in the model bacterial channel, SthK from Spirochaeta thermophila. We show that SthK is cold sensitive, displaying higher activity below 30 °C. Remarkably, SthK cold sensitivity depends strongly on membrane lipids, being sensitive in amine-containing lipids but insensitive in anionic lipids. Combining cryo-EM structural analysis, mutagenesis, and functional assays, we identify an intersubunit salt bridge that acts as temperature sensor. This salt bridge forms only in closed states, and determines channel opening by controlling closed-state stability. Lower temperatures weaken salt-bridge interactions, favoring channel opening, and lipid headgroups tune temperature sensitivity by modulating salt-bridge strength. These findings highlight how thermosensitivity can emerge from cooperative interactions between protein and the surrounding membrane.