MC4 crosslinking of rhodopsin and GRK1 complex

G protein-coupled receptor (GPCR) kinases (GRKs) selectively phosphorylate agonist bound GPCRs, thereby switching the signal from G protein-dependent to arrestin-dependent pathways, including receptor internalization and downregulation. There are currently no high-resolution details known about how a GRK recognizes an activated receptor, but most functional studies indicate that its unique N-terminus is key to agonist-dependent phosphorylation. Herein, we report the 7.2 Å cryo-electron microscopy (EM) single particle reconstruction of the rhodopsin-rhodopsin kinase (GRK1) complex. The structure reveals a 1:1 assembly with multiple contact points between the GRK1 kinase domain and rhodopsin, the most prominent being the insertion of the GRK1 N-terminal helix directly into the cytoplasmic cleft formed by rhodopsin in its active state. Cross-linking coupled with mass spectrometry, along with functional studies, confirmed the observed interface between the proteins and revealed regions of the complex that are dynamic.