Dr. Chakrapani's long-standing scientific interest has been in developing a molecular-level understanding of ion-transport phenomenon across cellular membranes that occurs under normal and pathophysiological conditions. Her research over the last 20 years has focused on ion channels that mediate fast synaptic transmission at the neuronal and neuromuscular junction. The pentameric Ligand-Gated Ion Channel (pLGIC) superfamily governs crucial physiological processes such as gastrointestinal functions, motor functions, and pain transmission. Aberrant channel functions are implicated in mood disorders, addiction, chronic pain, and cancer. Using cryo-electron microscopic approaches, her group seeks to determine high-resolution structural information about these clinically relevant drug-targets and their modulation by therapeutic agents.
Serotonin receptor (5-HT3AR), a member of the pLGIC, in the brain-gut circuitry directly control peristalsis, emetic reflex, and visceral pain perception. 5-HT3AR is the most common therapeutic target to manage nausea and vomiting during cancer therapies. Setrons, a class of competitive antagonists, cause functional inhibition of 5-HT3AR in the gastrointestinal tract and brainstem, are standard first-line of therapy as anti-emetic agents. Despite their prevalent use, the molecular mechanisms underlying setron binding and inhibition of 5-HT3AR are not fully understood. Further, refractory emesis and adverse side effects in some patients underscore the need to better therapeutics.
Using single-particle cryo-EM, Chakrapani's group solved structures of the full-length 5HT3AR in the resting state and two serotonin-activated conformations that revealed the molecular details of how serotonin activates the channel. Recently, they determined the structure of granisetron-bound 5-HT3AR to 2.92 Å resolution. The structure reveals the orientation of granisetron in the orthosteric site with unambiguous density for interacting sidechains. Molecular dynamics simulations and electrophysiology confirm the granisetron binding orientation and the residues central for ligand recognition. This new information is paving the way structure-based drug design of novel therapeutic agents that are safer and more effective.
Gibbs, E., Klemm, E., Seiferth, D., Kumar, A., Ilca, S. L., Biggin, P. C., & Chakrapani, S. (2023). Conformational transitions and allosteric modulation in a heteromeric glycine receptor. Nature communications, 14(1), 1363. https://doi.org/10.1038/s41467-023-37106-7 PMCID: PMC10011588
Kumar, A., Kindig, K., Rao, S., Zaki, A. M., Basak, S., Sansom, M. S. P., Biggin, P. C., & Chakrapani, S. (2022). Structural basis for cannabinoid-induced potentiation of alpha1-glycine receptors in lipid nanodiscs. Nature communications, 13(1), 4862. https://doi.org/10.1038/s41467-022-32594-5 PMCID: PMC9388682
Basak, S., Kumar, A., Ramsey, S., Gibbs, E., Kapoor, A., Filizola, M., & Chakrapani, S. (2020). High-resolution structures of multiple 5-HT3AR-setron complexes reveal a novel mechanism of competitive inhibition. eLife, 9, e57870. https://doi.org/10.7554/eLife.57870 PMCID: PMC7655109
Kumar, A., Basak, S., Rao, S., Gicheru, Y., Mayer, M. L., Sansom, M. S. P., & Chakrapani, S. (2020). Mechanisms of activation and desensitization of full-length glycine receptor in lipid nanodiscs. Nature communications, 11(1), 3752. https://doi.org/10.1038/s41467-020-17364-5 PMCID: PMC7385131
Basak, S., Gicheru, Y., Rao, S., Sansom, M. S. P., & Chakrapani, S. (2018). Cryo-EM reveals two distinct serotonin-bound conformations of full-length 5-HT3A receptor. Nature, 563(7730), 270–274. https://doi.org/10.1038/s41586-018-0660-7 PMCID: PMC6237196