This new understanding could lead to potential advances in pain therapy, the researchers said. Moreover, the scientists envision that their method may be potentially useful in studying the activation mechanism of other drugs and proteins.
"Because our ability to sense temperature is closely linked to our ability to sense pain, it is not surprising that the misregulation of temperature-activated ion channels can result in chronic pain syndromes," said Ardem Patapoutian, associate professor at Scripps Research and member of GNF, who directed the research. "In fact, some of these ion channels are considered targets to treat chronic inflammatory and neuropathic pain indications. Understanding how small molecules such as menthol affect the function of these proteins could be crucial in designing future drugs that can either activate or block them."
The study was released in an advanced online version by the journal Nature Neuroscience.
Utilizing a novel mutagenesis and high-throughput screening approach, the study assayed 14,000 TRPM8 mutants to find mutants that were not enhanced by menthol but were otherwise functioning normally. The scientists' analysis pinpointed a potential interaction site for menthol, as well as a site that translates binding information to ion channel activity.
Ion channels are proteins found in the cell membrane that can form a tunnel or channel that allows specific ions to move across the membrane. When activated, the channel opens, allowing an influx of calcium ions into the axon, an electrical signal that alerts the neuron, which relays the message to the brain.
Research Associate Michael Bandell, the lead author of the study, noted, "It's a well established method to mutate individual amino acid residues in an ion channel protein and examine the effect that these mutations have on the channel's function. However, the laborious nature of these experiments limits the number of mutant ion channels that can be made and analyzed. Our new high-throughput screening methodology allowed us to analyze 14,000 mutants out of which we isolated five that specifically affected menthol activity. Our experiments yielded significant insights into the functional elements of TRPM8 ion channel protein that would have been difficult to obtain using other mutagenesis methods."
Because the methodology can be used to screen for activation or inhibition, Bandell added, it could prove to be useful as a general method to analyze the mechanism by which drugs can activate or inhibit ion channels or other receptors. Specifically, the new methodology could be used to identify amino acid residues in certain ion channel proteins and G-protein coupled receptors (proteins involved in stimulus-response pathways) that are involved in the interaction with small molecules that affect their function.