Coupling to heterotrimers with C-terminal Gα subunit chimeras. Coupling to heterotrimers with C-terminal Gα subunit chimeras. Heat maps of ΔBRETmax (normalized to the largest value) for Gs-coupled (Top), Gi-coupled (second row), Gq-coupled (third row), and G12-coupled (Bottom) receptors. Maps are arranged from left to right depending on coupling that is determined more (e.g., H1R) or less (e.g., D1R) by the Gα C terminus (H5.17–H5.26). Each value represents the mean normalized ΔBRETmax from n = 3–6 independent experiments. Najeah Okashah et al. PNAS 2019;116:24:12054-12059 ©2019 by National Academy of Sciences