Biophysical Society Thematic Meeting | Bucharest 2026

Biophysics of Membrane Reactions in Brian

Poster Abstracts

15-POS Board 15 INFRARED SPECTROSCOPIC ANALYSIS OF NEGATIVE ALLOSTERIC MODULATION MECHANISMS IN MUSCARINIC ACETYLCHOLINE RECEPTORS Kento Watanabe 1 ; Yuya Sugiura 1 ; Moeka Mizuno 1 ; Akitoshi Inoue 2 ; Chiyo Suno 2 ; Ryoji Suno 2 ; Hideki Kandori 1,3 ; Kota Katayama 1,3 ; 1 Nagoya Institute of Technology, Grad. Sch. of Eng., Nagoya, Japan Negative allosteric modulation has emerged as a promising strategy for achieving subtype selective regulation of G protein–coupled receptors (GPCRs), particularly when orthosteric binding sites are highly conserved. In muscarinic acetylcholine receptors (mAChRs), which consist of five subtypes (M1R–M5R), selective modulation remains a central challenge in drug development. Although negative allosteric modulators (NAMs) have attracted increasing attention as potential therapeutic agents, the molecular mechanism by which they suppress receptor activity remains not fully understood. Structural characterization of NAM action is particularly difficult because the co-bound state of agonists and NAMs is often transient and unstable, limiting the applicability of static structural methods such as X-ray crystallography and cryo-electron microscopy. To overcome this limitation, we employed perfusion-induced FTIR difference spectroscopy, which enables sensitive detection of ligand-induced structural changes under near-physiological conditions. Using this approach, we previously characterized ligand recognition and activation mechanisms in the M2 receptor subtype. In the present study, we extend this method to investigate negative allosteric modulation in M1R/M2R. By monitoring dynamic structural responses upon NAM binding, we identify cooperative conformational changes that propagate from the allosteric site to functionally important regions of the receptor. These results provide molecular-level insight into how NAMs reduce receptor activity and demonstrate the utility of infrared spectroscopy for capturing dynamic regulatory mechanisms that are difficult to access by static structural approaches. 2 Kansai Medical University, Medical, Hirakata, Japan 3 OptoBio Technology Research Center, Nagoya, Japan

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