Development of Plug and Play'' Fiducial Marks for Structural Studies of GPCR Signaling Complexes by Single-Particle Cryo-EM

Universal'' synthetic antibody (sAB)-based fiducial marks have been generated by customized phage display selections to facilitate the rapid structure determination of G protein-coupled receptor (GPCR) signaling complexes by single-particle cryo-electron microscopy (SP cryo-EM). sABs were generated to the two major G protein subclasses: trimeric G(i) and G(s), as well as mini-G(s), and were tested to ensure binding in the context of their cognate GPCRs. Epitope binning revealed that multiple distinct epitopes exist for each G(alpha beta gamma) protein. Several G beta gamma-specific sABs, cross-reactive between trimeric G(i) and G(s), were identified suggesting they could be used across all subclasses in a plug and play'' fashion. sABs were also generated to a representative of another class of GPCR signaling partner, G protein receptor kinase 1 (GRK1) and evaluated further, supporting the generalizability of the approach. EM data suggested that the subclass-specific sABs provide effective single and dual fiducials for multiple GPCR signaling complexes.