# Probing the structure and function of the intracellular domain of cys-loop receptors

> **NIH NIH R01** · TEXAS TECH UNIVERSITY HEALTH SCIS CENTER · 2024 · $371,025

## Abstract

Project Summary
Pentameric ligand-gated ion channels (pLGICs), also called Cys-loop receptors in eukaryotes, include the
receptors for acetylcholine, serotonin, GABA and glycine. They are involved in numerous neuropsychiatric,
neurologic, and inflammatory diseases. All Cys-loop receptor family members in metazoans contain three
structural domains: an extracellular domain (ECD), a transmembrane domain (TMD), and an intracellular domain
(ICD). The ECD and TMD are architecturally conserved between receptor families. The ICD is poorly conserved
in both length and amino-acid composition and, for many subunits, contains large regions of predicted structural
disorder. Due to the challenge of working with the ICDs of pentameric receptors, they have been essentially
overlooked in terms of rigorous mechanistic characterization and direct exploration as pharmacological targets.
The ICD is involved in finetuning plasma membrane expression levels, targeting, and function, in part mediated
by protein-protein interactions (PPI) for example with chaperones. We envision that mechanistic knowledge of
chaperone-mediated modulation will uncover new PPI drug targets. Through our published studies of the ICD
we defined a linker that allowed for structure determination of the first in class structures of homo- and
heteropentameric GABAA receptors. We also established that the ICD alone assembles into pentamers,
establishing a novel role for the ICD in oligomeric assembly. Here, we propose a multi-layered approach
leveraging both soluble ICD chimeras and full-length receptors together with results obtained during the
previous funding period in careful consideration of recently-published pLGIC structures. We discovered that the
resistance to inhibitors of choline esterase (Ric-3) chaperone binds to a 24-amino acid L1-MX segment of 5-HT3A
subunits. With the new proposed specific aims (SA) we will: (SA1) determine the role of the L1-MX segment in
RIC-3 modulation of cationic pLGIC assembly, (SA2) identify novel protein-protein interactions mediated via
cationic ICDs, and (SA3) characterize the mechanism by which opening of cation-conducting pLGICs involves
translocation of the L1-MX segment through the MA-helix framed portals. In each aim, we will use biochemical
and electrophysiological methods, coupled with overexpressed and purified proteins or proteins in their cellular
environment. We anticipate that our studies will provide the basis for a novel class of targets for therapeutic
development, PPI modulators for pentameric channel intracellular domains.

## Key facts

- **NIH application ID:** 10746829
- **Project number:** 5R01NS077114-08
- **Recipient organization:** TEXAS TECH UNIVERSITY HEALTH SCIS CENTER
- **Principal Investigator:** Michaela Jansen
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $371,025
- **Award type:** 5
- **Project period:** 2021-12-15 → 2025-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10746829

## Citation

> US National Institutes of Health, RePORTER application 10746829, Probing the structure and function of the intracellular domain of cys-loop receptors (5R01NS077114-08). Retrieved via AI Analytics 2026-06-01 from https://api.ai-analytics.org/grant/nih/10746829. Licensed CC0.

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