Researchers at the University of Basel have used an advanced NMR-based triangulation technique to map the motions of a key membrane protein at atomic resolution. By refining and applying paramagnetic labelling strategies previously established for structural biology, the team tracked conformational dynamics in a G protein-coupled receptor (GPCR) – a major class of drug targets. The results, published in Science, provide a detailed view of receptor behaviour with implications for drug development.
GPCRs regulate a wide range of physiological processes and are the targets of around one-third of all approved drugs. Yet the structural transitions that link ligand binding to intracellular signalling have remained incompletely understood.
“We knew little about how GPCRs transmit the information from the various ligands,” said Dr. Fengjie Wu, SNSF Ambizione Fellow at the Biozentrum, University of Basel, Switzerland, in the press release. “We developed this method that allows us to observe how the receptor moves.”
In this study, the researchers focused on the β1-adrenergic receptor, a cardiovascular GPCR targeted by beta-blockers. Using triple-site paramagnetic labelling on a monoclonal antibody that binds the receptor, they measured around 100 atomic positions with sub-angstrom precision. This approach combines pseudocontact shifts and paramagnetic relaxation enhancements to triangulate positions within the protein – analogous to how GPS determines geographic location.
Rather than behaving as a binary switch, the receptor was shown to sample a range of conformational states – including inactive, preactive, and active forms. Ligands such as isoprenaline and carazolol were observed to shift the population of these states in different directions. “We finally can tell with confidence how the receptor transitions between its functional states,” Wu said. “We could even define a highly conserved central microswitch that controls these states.”
The triangulation strategy allowed the team to bridge the gap between static crystal structures and the dynamic states proteins adopt in action. “After twenty years of efforts, we can finally see very fine details of the receptor motions,” said Professor Stephan Grzesiek, senior author of the study.
In addition, the researchers found that minor atomic-level changes could fine-tune signalling outcomes. “To truly understand how these receptors work, it is essential to go down to the atomic level and to observe the motions in response to perturbations,” Wu said. “With these observations, we now understand the basic mechanism of how drug binding regulates the receptor. This knowledge may provide guidance for designing drugs with desired outputs.”
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