Amrita Samanta

Cryo-EM structure of 5-HT3A receptor in its resting conformation

Serotonin receptors (5-HT3AR) directly regulate gut movement, and drugs that inhibit 5-HT3AR function are used to control emetic reflexes associated with gastrointestinal pathologies and cancer therapies. The 5-HT3AR function involves a finely tuned orchestration of three domain movements that include the ligand-binding domain, the pore domain, and the intracellular domain. Here, we present the structure from the full-length 5-HT3AR channel in the apo-state determined by single-particle cryo-electron microscopy at a nominal resolution of 4.3 Å. In this conformation, the ligand-binding domain adopts a conformation reminiscent of the unliganded state with the pore domain captured in a closed conformation. In comparison to the 5-HT3AR crystal structure, the full-length channel in the apo-conformation adopts a more expanded conformation of all the three domains with a characteristic twist that is implicated in gating.Serotonin receptor (5-HT3AR), a pentameric ligand-gated ion channel, regulates numerous gastrointestinal functions. Here the authors provide a cryo-electron microscopic structure from the full-length 5-HT3AR in the apo-state which corresponds to a resting conformation of the channel.

Structural insights into the molecular mechanism of mouse TRPA1 activation and inhibition

Pain, though serving the beneficial function of provoking a response to dangerous situations, is an unpleasant sensory and emotional experience. Transient receptor potential ankyrin 1 (TRPA1) is a member of the transient receptor potential (TRP) cation channel family and is localized in “nociceptors,” where it plays a key role in the transduction of chemical, inflammatory, and neuropathic pain. TRPA1 is a Ca2+-permeable, nonselective cation channel that is activated by a large variety of structurally unrelated electrophilic and nonelectrophilic chemical compounds. Electrophilic ligands are able to activate TRPA1 channels by interacting with critical cysteine residues on the N terminus of the channels via covalent modification and/or disulfide bonds. Activation by electrophilic compounds is dependent on their thiol-reactive moieties, accounting for the structural diversity of the group. On the other hand, nonelectrophilic ligands do not interact with critical cysteines on the channel, so the structural diversity of this group is unexplained. Although near-atomic-resolution structures of TRPA1 were resolved recently by cryo-electron microscopy, in the presence of both agonists and antagonists, detailed mechanisms of channel activation and inhibition by these modulators could not be determined. Here, we investigate the effect of both electrophilic and nonelectrophilic ligands on TRPA1 channel conformational rearrangements with limited proteolysis and mass spectrometry. Collectively, our results reveal that channel modulation results in conformational rearrangements in the N-terminal ankyrin repeats, the pre-S1 helix, the TRP-like domain, and the linker regions of the channel.