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

Area of Science:

• Biochemistry
• Structural Biology
• Pharmacology

Background:

• Understanding G protein-coupled receptor (GPCR) intermediate complexes is crucial for drug development.
• Existing structural data predominantly shows fully activated GPCR-G protein complexes, leaving intermediate states poorly understood.

Purpose of the Study:

• To determine the structure of an intermediate GPCR-G protein complex.
• To investigate the functional role of this intermediate complex in initiating signaling.

Main Methods:

• Utilized 19F quantitative NMR and molecular dynamics (MD) simulations to map conformational landscapes.
• Employed cryo-electron microscopy (cryo-EM) to determine the structure of the intermediate complex at 2.8 Å resolution.
• Blocked the transition to the fully activated state to capture the intermediate.

Main Results:

• Determined the cryo-EM structure of an intermediate GPCR-mini-Gαsβγ complex.
• Provided direct evidence that the intermediate complex drives a rate-limited nucleotide exchange.
• Observed partial opening of the Gα's α-helical domain (AHD) engaged by a second nucleotide, supported by MD simulations.

Conclusions:

• The intermediate complex represents a distinct functional state in GPCR signaling.
• This intermediate complex can initiate nucleotide exchange independently of full activation.
• These findings bridge a critical knowledge gap in GPCR signaling mechanisms and drug discovery.