Submolecular probing of the complement C5a receptor–ligand binding reveals a cooperative two-site binding mechanism

• Published in: Communications biology 2020-12, Vol.3 (1), p.786-786, Article 786
• Main Authors: Dumitru, Andra C., Deepak, R. N. V. Krishna, Liu, Heng, Koehler, Melanie, Zhang, Cheng, Fan, Hao, Alsteens, David
• Format: Article
• Language: English
• Subjects: 631/1647/2204/1262; 631/57/2282; 9/10; Atomic force microscopy; Binding sites; Biology; Biomedical and Life Sciences; Cell activation; Cell surface; Complement component C5a; Cooperativity; G protein-coupled receptors; Life Sciences; Ligands; Macromolecules; Molecular dynamics; N-Terminus
• ISSN: 2399-3642; 2399-3642
• DOI: 10.1038/s42003-020-01518-8

A current challenge to produce effective therapeutics is to accurately determine the location of the ligand-biding site and to characterize its properties. So far, the mechanisms underlying the functional activation of cell surface receptors by ligands with a complex binding mechanism remain poorly understood due to a lack of suitable nanoscopic methods to study them in their native environment. Here, we elucidated the ligand-binding mechanism of the human G protein-coupled C5a receptor (C5aR). We discovered for the first time a cooperativity between the two orthosteric binding sites. We found that the N -terminus C5aR serves as a kinetic trap, while the transmembrane domain acts as the functional site and both contributes to the overall high-affinity interaction. In particular, Asp282 plays a key role in ligand binding thermodynamics, as revealed by atomic force microscopy and steered molecular dynamics simulation. Our findings provide a new structural basis for the functional and mechanistic understanding of the GPCR family that binds large macromolecular ligands. Dumitru et al. probe the ligand-binding mechanism and activation of the human G protein-coupled C5a receptor (C5aR) and discover a cooperativity between the two orthosteric binding sites. Their findings, probing the dynamic aspects of receptor–ligand interaction, are valuable to develop a better understanding of GPCR activation and signalling.