Cryo-Electron Microscopy Captures the Body's Cold Sensor Transitioning From Closed to Open
Pop a mint into your mouth and your brain interprets the sensation as cool. Step into a cold shower and it fires the same signal. In both cases, the molecular trigger is a protein channel called TRPM8 - a structure embedded in sensory neuron membranes that opens in response to temperatures between roughly 46 and 82 degrees Fahrenheit, as well as to menthol and related chemical compounds. Scientists have known for two decades that TRPM8 is the body's primary cold detector. Until now, no one had seen in structural detail exactly how it works.
Researchers from Seok-Yong Lee's laboratory at Duke University, presenting findings at the 70th Biophysical Society Annual Meeting, used cryo-electron microscopy to capture multiple conformational states of TRPM8 as it moves from its closed resting configuration to its open, ion-conducting state. The images represent the first molecular-resolution snapshots of this transition and reveal that cold and menthol activate the channel through partially overlapping but distinct structural pathways.
A Microscope for Frozen Proteins
Cryo-electron microscopy works by rapidly freezing proteins in a thin film of vitreous ice, then imaging them with a beam of electrons. This preserves the protein in near-physiological conformations without the artifacts that can arise from crystal packing in traditional X-ray crystallography. The technique has transformed structural biology over the past decade, enabling high-resolution structures of membrane proteins - including ion channels - that were previously inaccessible.
TRPM8 is a tetrameric channel, meaning four identical protein subunits assemble together to form a single functional unit. The assembled structure spans the cell membrane, with a central pore that opens or closes to regulate the flow of ions - primarily calcium and sodium - into the cell. Ion flow generates an electrical signal that propagates along the nerve to the brain, producing the subjective sensation of cold or chemical cooling.
Cold and Menthol Activate Through Different Routes
Hyuk-Joon Lee, a postdoctoral fellow in the Seok-Yong Lee laboratory and the study's lead researcher, described the key finding: "Menthol is like a trick. It attaches to a specific part of the channel and triggers it to open, just like cold temperature would. So even though menthol isn't actually freezing anything, your body gets the same signal as if it were touching ice."
The structural data show that this is not just functionally true but mechanistically distinct. Cold temperature primarily triggers conformational changes in the pore-forming region of the channel - the section that physically opens to allow ion flow. Menthol binds to a different site and induces shape changes that propagate through the protein's structure to reach the pore. Both pathways converge on the same outcome - channel opening - but they get there differently.
The combination of both stimuli enhances the response synergistically. This is physiologically relevant: menthol applied to cold skin produces a cooling sensation that is more intense than either stimulus alone would predict. The structural data suggest this enhancement reflects genuine cooperativity between the two activation pathways. The researchers exploited this synergy experimentally, using cold combined with menthol to capture TRPM8 in its fully open conformation - something that neither stimulus alone had achieved in prior structural studies.
A Cold Spot and Medical Applications
The team also identified a specific region of TRPM8 they describe as a "cold spot" - a portion of the protein uniquely important for temperature sensing that helps prevent the channel from desensitizing during prolonged cold exposure. Desensitization is a common feature of sensory receptors: they reduce their response over time as a stimulus continues. The cold spot appears to counteract this tendency in TRPM8, which is consistent with the clinical observation that prolonged cold exposure does not produce complete analgesia in the way that sustained stimulation can silence other sensory receptors.
TRPM8 dysfunction has been linked to several medical conditions. Chronic pain, migraines, and certain cancers show altered TRPM8 expression or function. On the therapeutic side, acoltremon - a drug that activates TRPM8 - is an FDA-approved eye drop for dry eye disease. It works by activating the cooling pathway in corneal sensory neurons to stimulate tear production and reduce irritation. Understanding the structural basis of menthol-like activation at TRPM8 could guide the design of more potent or selective activators for conditions where the pathway has therapeutic value.
The work is preclinical and structural in character. It does not propose new treatments directly. What it provides is a mechanistic foundation - a precise picture of how a clinically important protein works at the molecular level - that can guide drug discovery efforts, help explain why existing TRPM8-targeting drugs have the properties they do, and support rational design of compounds with improved profiles.