Extended Data Fig. 1: Summary of cryo-EM data processing.

Details are found in the methods. In short, 2680 micrographs were collected on a Krios equipped with Gatan K2 direct electron detector. Heterogeneous refinement was used to remove junk, with 2D classification as a form of verification. Once an ideal particle stack was identified, subsequent rounds of heterogeneous refinement were combined with local CTF refinement and Bayesian polishing to further improve the map. Local refinements of b1-AR and Gi helped bring out features in the periphery of the structure. The model was built into the consensus and local refinements, and then used to generate a composite map that was used for the final round of real-space refinement. Overall, even in the consensus structure, almost all of the model was well represented by density. The alpha-helical domain was less well resolved due to flexibility, but intermediate resolution rigid-body docking was possible.