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Structural and Evolutionary Insights Point to Allosteric Regulation of TRP Ion Channels.

ABSTRACT: The familiar pungent taste of spicy food, the refreshing taste of mint, and many other physiological phenomena are mediated by transient receptor potential (TRP) ion channels. TRP channels are a superfamily of ion channels that are sensitive to diverse chemical and physical stimuli and play diverse roles in biology. In addition to chemical regulation, some family members also sense common physical stimuli, such as temperature or pressure. Since their discovery and cloning in the 1990s and 2000s, understanding the molecular mechanisms governing TRP channel function and polymodal regulation has been a consistent but challenging goal. Until recently, a general lack of high-resolution TRP channel structures had significantly limited a molecular understanding of their function. In the past few years, a flood of TRP channel structures have been released, made possible primarily by advances in cryo-electron microscopy (cryo-EM). The boon of many structures has unleashed unparalleled insight into TRP channel architecture. Substantive comparative studies between TRP structures provide snapshots of distinct states such as ligand-free, stabilized by chemical agonists, or antagonists, partially illuminating how a given channel opens and closes. However, the now ∼75 TRP channel structures have ushered in surprising outcomes, including a lack of an apparent general mechanism underlying channel opening and closing among family members. Similarly, the structures reveal a surprising diversity in which chemical ligands bind TRP channels. Several TRP channels are activated by temperature changes in addition to ligand binding. Unraveling mechanisms of thermosensation has proven an elusive challenge to the field. Although some studies point to thermosensitive domains in the transmembrane region of the channels, results have sometimes been contradictory and difficult to interpret; in some cases, a domain that proves essential for thermal sensitivity in one context can be entirely removed from the channel without affecting thermosensation in another context. These results are not amenable to simple interpretations and point to allosteric networks of regulation within the channel structure. TRP channels have evolved to be fine-tuned for the needs of a species in its environmental niche, a fact that has been both a benefit and burden in unlocking their molecular features. Functional evolutionary divergence has presented challenges for studying TRP channels, as orthologs from different species can give conflicting experimental results. However, this diversity can also be examined comparatively to decipher the basis for functional differences. As with structural biology, untangling the similarities and differences resulting from evolutionary pressure between species has been a rich source of data guiding the field. This Account will contextualize the existing biochemical and functional data with an eye to evolutionary data and couple these insights with emerging structural biology to better understand the molecular mechanisms behind chemical and physical regulation of TRP channels.

SUBMITTER: Hilton JK

PROVIDER: S-EPMC8628317 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundTRP (Transient Receptor Potential) channels respond to diverse stimuli and thus function as the primary integrators of varied sensory information. They are also activated by various compounds and secondary messengers to mediate cell-cell interactions as well as to detect changes in the local environment. Their physiological roles have been primarily characterized only in mice and fruit flies, and evolutionary studies are limited. To understand the evolution of insect TRP channels and the mechanisms of integrating sensory inputs in insects, we have identified and compared TRP channel genes in Drosophila melanogaster, Bombyx mori, Tribolium castaneum, Apis mellifera, Nasonia vitripennis, and Pediculus humanus genomes as part of genome sequencing efforts.ResultsAll the insects examined have 2 TRPV, 1 TRPN, 1 TRPM, 3 TRPC, and 1 TRPML subfamily members, demonstrating that these channels have the ancient origins in insects. The common pattern also suggests that the mechanisms for detecting mechanical and visual stimuli and maintaining lysosomal functions may be evolutionarily well conserved in insects. However, a TRPP channel, the most ancient TRP channel, is missing in B. mori, A. mellifera, and N. vitripennis. Although P. humanus and D. melanogaster contain 4 TRPA subfamily members, the other insects have 5 TRPA subfamily members. T. castaneum, A. mellifera, and N. vitripennis contain TRPA5 channels, which have been specifically retained or gained in Coleoptera and Hymenoptera. Furthermore, TRPA1, which functions for thermotaxis in Drosophila, is missing in A. mellifera and N. vitripennis; however, they have other Hymenoptera-specific TRPA channels (AmHsTRPA and NvHsTRPA). NvHsTRPA expressed in HEK293 cells is activated by temperature increase, demonstrating that HsTRPAs function as novel thermal sensors in Hymenoptera.ConclusionThe total number of insect TRP family members is 13-14, approximately half that of mammalian TRP family members. As shown for mammalian TRP channels, this may suggest that single TRP channels are responsible for integrating diverse sensory inputs to maintain the insect sensory systems. The above results demonstrate that there are both evolutionary conservation and changes in insect TRP channels. In particular, the evolutionary processes have been accelerated in the TRPA subfamily, indicating divergence in the mechanisms that insects use to detect environmental temperatures.

Project description:BackgroundEtomidate is a preferred drug for the induction of general anesthesia in cardiovascular risk patients. As with propofol and other perioperatively used anesthetics, the application of aqueous etomidate formulations causes an intensive burning pain upon injection. Such algogenic properties of etomidate have been attributed to the solubilizer propylene glycol which represents 35% of the solution administered clinically. The aim of this study was to investigate the underlying molecular mechanisms which lead to injection pain of aqueous etomidate formulations.ResultsActivation of the nociceptive transient receptor potential (TRP) ion channels TRPA1 and TRPV1 was studied in a transfected HEK293t cell line by whole-cell voltage clamp recordings of induced inward ion currents. Calcium influx in sensory neurons of wild-type and trp knockout mice was ratiometrically measured by Fura2-AM staining. Stimulated calcitonin gene-related peptide release from mouse sciatic nerves was detected by enzyme immunoassay. Painfulness of different etomidate formulations was tested in a translational human pain model. Etomidate as well as propylene glycol proved to be effective agonists of TRPA1 and TRPV1 ion channels at clinically relevant concentrations. Etomidate consistently activated TRPA1, but there was also evidence for a contribution of TRPV1 in dependence of drug concentration ranges and species specificities. Distinct N-terminal cysteine and lysine residues seemed to mediate gating of TRPA1, although the electrophile scavenger N-acetyl-L-cysteine did not prevent its activation by etomidate. Propylene glycol-induced activation of TRPA1 and TRPV1 appeared independent of the concomitant high osmolarity. Intradermal injections of etomidate as well as propylene glycol evoked severe burning pain in the human pain model that was absent with emulsification of etomidate.ConclusionsData in our study provided evidence that pain upon injection of clinical aqueous etomidate formulations is not an unspecific effect of hyperosmolarity but rather due to a specific action mediated by activated nociceptive TRPA1 and TRPV1 ion channels in sensory neurons.

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Structural and Evolutionary Insights Point to Allosteric Regulation of TRP Ion Channels.

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