Structural insights into TRPM8 inhibition and desensitization

Abstract

The transient receptor potential melastatin 8 (TRPM8) ion channel is the primary detector of environmental cold and an important target for treating pathological cold hypersensitivity. Here, we present cryo–electron microscopy structures of TRPM8 in ligand-free, antagonist-bound, or calcium-bound forms, revealing how robust conformational changes give rise to two nonconducting states, closed and desensitized. We describe a malleable ligand-binding pocket that accommodates drugs of diverse chemical structures, and we delineate the ion permeation pathway, including the contribution of lipids to pore architecture. Furthermore, we show that direct calcium binding mediates stimulus-evoked desensitization, clarifying this important mechanism of sensory adaptation. We observe large rearrangements within the S4-S5 linker that reposition the S1-S4 and pore domains relative to the TRP helix, leading us to propose a distinct model for modulation of TRPM8 and possibly other TRP channels.

Structural basis for human TRPC5 channel inhibition by two distinct inhibitors

“…Indeed, AM-1473, a potent antagonist of hTRPC6 were found to bind at IBP-A in hTRPC6 as well ( 44 ). Moreover, IBP-A is the AMTB and TC-I 2014 binding sites in TRPM8 ( 45 ), 2-APB binding site in TRPV6 ( 46 ) (Fig. S7A).…”

A paradigm of thermal adaptation in penguins and elephants by tuning cold activation in TRPM8

“…From the perspective of channel structure, an earlier study suggested that its C terminus is crucial for cold activation (10), while subsequent work demonstrated that the transmembrane core domain (5) or the pore domain (11) is essential for setting cold response. Although high-resolution structures of TRPM8 have been resolved by cryoelectron microscopy in both the apo and ligand-bound states (12)(13)(14), its coldactivated state structure is still unavailable. From the perspective of thermodynamics, large enthalpic (ΔH) and entropic (ΔS) changes are associated with TRPM8 cold activation (15,16).…”

Structural mechanisms of transient receptor potential ion channels

“…Such a transition from a low- to high-energy state, on the surface, is counterintuitive, but it can be rationalized that the high-energy π-helix is compensated by formation of new hydrophilic interactions within its neighboring regions (McGoldrick et al, 2018). Similarly, an α- to π-helix transition in S6 accompanies the transition from a closed to sensitized or open state in TRPV3 (Singh et al, 2018a; Zubcevic et al, 2018a, 2019), and from a closed to desensitized state in TRPM8 (Diver et al, 2019). We found that a gain-of-function (F604P) mutation in PKD2 leads to an opposite π- to α-helix transition, resulting in dilation of the lower gate that might underlie constitutive channel activity of this mutant (Arif Pavel et al, 2016; Zheng et al, 2018).…”

“…In TRPM2, TRPM4, TRPM8, and TRPA1 structures, a Ca 2+ ion is coordinated by hydrophilic residues at an equivalent site (Guo et al, 2017; Winkler et al, 2017; Autzen et al, 2018; Duan et al, 2018c; Huang et al, 2018; Wang et al, 2018; Yin et al, 2018; Zhang et al, 2018b; Yin et al, 2019a,b; Zhao et al, 2019); this Ca 2+ -binding site is essential for activation of TRPM8 by a cooling compound icilin, as well as for activation and desensitization of TRPA1 downstream of metabotropic receptors (Yin et al, 2019a; Zhao et al, 2019). In TRPM8, this pocket appears to be malleable to also accommodate both antagonists and agonists of diverse chemical structures (Diver et al, 2019; Yin et al, 2019a). Moreover, in TRPC4, a non-protein density at a similar hydrophilic pocket was tentatively modeled as a Na + ion, the predominant ion in the specimen used for structure determination (Duan et al, 2018a).…”

“…Second, the selectivity filter and outer pore loops of TRPM8 are surprisingly invisible in a closed state. Interestingly, both the S4–S5 linker and selectivity filter are well-defined in a desensitized state in TRPM8 (Diver et al, 2019), hinting that these structure elements are likely more dynamic as compared to TRPM2 channels. Whether such structural differences reflect a genuinely distinct design principle for cold- and heat-sensitive TRPM channels remains to be determined.…”