Structural snapshots of TRPV1 reveal mechanism of polymodal functionality

Abstract

Many transient receptor potential (TRP) channels respond to diverse stimuli and conditionally conduct small and large cations. Such functional plasticity is presumably enabled by a uniquely dynamic ion selectivity filter that is regulated by physiological agents. What is currently missing is a ''photo series'' of intermediate structural states that directly address this hypothesis and reveal specific mechanisms behind such dynamic channel regulation. Here, we exploit cryoelectron microscopy (cryo-EM) to visualize conformational transitions of the capsaicin receptor, TRPV1, as a model to understand how dynamic transitions of the selectivity filter in response to algogenic agents, including protons, vanilloid agonists, and peptide toxins, permit permeation by small and large organic cations. These structures also reveal mechanisms governing ligand binding substates, as well as allosteric coupling between key sites that are proximal to the selectivity filter and cytoplasmic gate. These insights suggest a general framework for understanding how TRP channels function as polymodal signal integrators. ll

Structural Plasticity of the Selectivity Filter in Cation Channels

“…The SF structures include various constricted, stable conformations as well as asymmetric or even disordered states (see Figure 2 ). Recently, the TRPV1 and the HCN4 pore loop channels were discovered to have more subtle structural plasticity of the SF in their ability to adapt to different ion types ( Saponaro et al, 2021 ; Zhang et al, 2021 ).…”

Druggable Lipid Binding Sites in Pentameric Ligand-Gated Ion Channels and Transient Receptor Potential Channels

“…When a vanilloid binds, this pocket re-arranges such that R557 interacts with E570 within the S4-S5 linker pulling the S4-S5 linker, S5 and S6 away from the central axis and opening the channel pore (Figure 7A). A recent cryo-EM study showing multiple snapshots of TRPV1 demonstrates stepwise displacement of the PI acyl chains by RTX followed by the PI headgroup (Zhang et al, 2021a). Visualization of these intermediates shows that PI lipids from all four subunits must be displaced to produce conformational changes in S5 and S6 associated with channel opening.…”

Applications of Cryo-EM in small molecule and biologics drug design

“…As the selection of grids, ice, and particles becomes better optimized, the computational burden of filtering good from bad particles is reduced, and we anticipate that further streamlining will continue to reduce computational needs and speed data processing. Recent iterations of data processing software have included improved tools for processing particles with inter-domain flexibility or conformational changes, even in the absence of discrete structural states, allowing higher-resolution modeling of proteins in multiple conformations and analysis of their conformational dynamics [90][91][92], with even time-resolved structures beginning to emerge [93,94].…”