Mutations of TRPM8 channels: Unraveling the molecular basis of activation by cold and ligands

Abstract

The cation nonselective channel TRPM8 is activated by multiple stimuli, including moderate cold and various chemical compounds (i.e., menthol and icilin [Fig. 1], among others). While research continues growing on the understanding of the physiological involvement of TRPM8 channels and their role in various pathological states, the information available on its activation mechanisms has also increased, supported by mutagenesis and structural studies. This review compiles known information on specific mutations of channel residues and their consequences on channel viability and function. Besides, the comparison of sequence of animals living in different environments, together with chimera and mutagenesis studies are helping to unravel the mechanism of adaptation to different temperatures. The results of mutagenesis studies, grouped by different channel regions, are compared with the current knowledge of TRPM8 structures obtained by cryo-electron microscopy. Trying to make this review self-explicative and highly informative, important residues for TRPM8 function are summarized in a figure, and mutants, deletions and chimeras are compiled in a table, including also the observed effects by different methods of activation and the corresponding references. The information provided by this review may also help in the design of new ligands for TRPM8, an interesting biological target for therapeutic intervention.

Keywords: TRPM8; agonist; antagonists; mutants; structure.

Figure 1

Menthol and TRPM8 agonists and antagonists present in cryo‐EM structures of TRPM8,

Figure 2

Schematic representation of the transmembrane region of TRPM8 (extracted from PDB ID 6O77 cryo‐EM structure) [Color figure can be viewed at wileyonlinelibrary.com]

Figure 3

Summary of important residues in TRPM8 function identified in mutagenesis studies. Upon mutation of a given residue, colored circles indicate disrupted processes as shown by legend. The hsTRPM8 sequence has been used to integrate information from every studied species. Cylinders indicated α‐helices based on the secondary structure analysis of the different structures deposited in the Protein Data Bank [Color figure can be viewed at wileyonlinelibrary.com]

Figure 4

View of faTRPM8 in complex with ligands. On the left, view of faTRPM8 in complex with menthol analog WS‐12 (PDB ID 6NR2), on the right, view of faTRPM8 in complex with icilin (PDB ID 6NR3). For clarity only residues included in the text are shown. Polar interactions are depicted as orange dashes lines. Ca²⁺ ion is depicted as a green sphere. Residue numbers in faTRPM8 (dark gray), in hsTRPM8 (brown) [Color figure can be viewed at wileyonlinelibrary.com]

Figure 5

View of the pore domain residues that have been mutated (pmTRPM8 structure, PDB ID 6O77). Residue numbers corresponding to pmTRPM8 (dark gray) and to hsTRPM8 (brown). Polar interactions are depicted as dotted orange lines [Color figure can be viewed at wileyonlinelibrary.com]