Decoding the structural basis of ligand recognition and biased signaling in the motilin receptor

  • Cell Rep. 2025 Mar 25;44(3):115329. doi: 10.1016/j.celrep.2025.115329.
Chongzhao You  1 ,  Mengting Jiang  2 ,  Tianyu Gao  3 ,  Zining Zhu  4 ,  Xinheng He  5 ,  Youwei Xu  5 ,  Yuan Gao  5 ,  Yi Jiang  6 ,  H Eric Xu  7
Affiliations
  • 1. The State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China; University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: [email protected].
  • 2. Lingang Laboratory, Shanghai 200031, China; School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China.
  • 3. The State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China; School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China.
  • 4. School of Chinese Materia Medica, Nanjing University of Chinese Medicine, Nanjing 210046, China.
  • 5. The State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China; University of Chinese Academy of Sciences, Beijing 100049, China.
  • 6. Lingang Laboratory, Shanghai 200031, China; School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China. Electronic address: [email protected].
  • 7. The State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China; University of Chinese Academy of Sciences, Beijing 100049, China; Lingang Laboratory, Shanghai 200031, China; School of Chinese Materia Medica, Nanjing University of Chinese Medicine, Nanjing 210046, China; School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China. Electronic address: [email protected].
PMID: 39987561 DOI: 10.1016/j.celrep.2025.115329
Abstract

The Motilin Receptor (MTLR) is a key target for treating gastrointestinal (GI) disorders like gastroparesis, yet developing effective agonists remains challenging due to drug tolerance and signaling bias. We present cryoelectron microscopy (cryo-EM) structures of MTLR bound to azithromycin, a macrolide Antibiotic, and DS-3801b, a non-macrolide agonist. Distinct ligand recognition mechanisms are revealed, with azithromycin binding deeply within the orthosteric pocket and DS-3801b adopting a special clamp-like conformation stabilized by a water molecule. We also highlight the critical role of extracellular loop 2 (ECL2) in ligand specificity and signaling pathway activation, affecting both G-protein and β-arrestin signaling. Additionally, the "D2.60R2.63S3.28" motif and interactions around transmembranes 6/7 (TM6/7) are identified as key drivers of signaling selectivity. These findings offer insights into the structural dynamics of MTLR, laying the groundwork for the rational design of next-generation GI prokinetic drugs with enhanced efficacy and safety.

Keywords
CP: Molecular biology; DS-3801b; GPCR; azithromycin; biased signaling; macrolide antibiotics; motilin receptor; structural biology.
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