# Structure and function of a ligand-free GPCR-Gαβγ intermediate complex

## TL;DR

Scientists discovered a new intermediate complex in GPCR signaling using cryo-EM and simulations, revealing how it initiates nucleotide exchange before full activation.

## Contribution

The study reveals the structure and function of a ligand-free GPCR-Gαβγ intermediate complex and its role in nucleotide exchange.

## Key findings

- The intermediate GPCR-Gαsβγ complex structure was determined at 2.8 Å resolution using cryo-EM.
- The intermediate complex initiates nucleotide exchange without progressing to full activation.
- MD simulations confirmed the partial opening of the Gα's α-helical domain during this process.

## Abstract

Unraveling the signaling roles of intermediate complexes is pivotal for G protein-coupled receptor (GPCR) drug development. Despite hundreds of GPCR-Gαβγ structures, these snapshots primarily capture the fully activated complex. Consequently, the functions of intermediate GPCR-G protein complexes remain elusive. Guided by a conformational landscape visualized via 19F quantitative NMR and molecular dynamics (MD) simulation, we determined the structure of an intermediate GPCR-mini-Gαsβγ complex at 2.8 Å using cryo-EM, by blocking its transition to the fully activated complex. Furthermore, we presented direct evidence that the intermediate complex initiates a rate-limited nucleotide exchange without progressing to the fully activated complex, in which the α-helical domain (AHD) of the Gα is partially open engaged by a second nucleotide. Our MD simulation supported the pose of the AHD domain. These advances bridge a significant gap in our understanding the complexity of GPCR signaling.