Native Mass Spectrometry Reveals Ligand-Specific Conformational Heterogeneity of the β₁‑Adrenergic Receptor Using Nanobody Probes

While emerging evidence highlights a critical link between ligand-induced receptor conformations and pharmacological outcomes, the structural diversity dictating GPCR-G protein interface interactions remains incompletely understood. High-resolution structural studies reveal discrete, ligand-stabilized states, but these static snapshots do not fully capture the dynamic processes underlying GPCR activation and ligand efficacy.

To address this, we established a native mass spectrometry (nMS) platform to probe ligand-induced conformational heterogeneity at the GPCR intracellular interface. Using the β1-adrenergic receptor (β₁AR) as a model, we demonstrated a strong correlation between ligand efficacy and receptor complex formation with diverse active-state-specific nanobodies. Notably, leveraging the quantitative capacity of nMS, we uncovered distinct propensities of two highly similar nanobodies, Nb80 and Nb6B9, and showed that Nb6B9 engages weak-agonist-stabilized receptor states more effectively than Nb80.