Sequence of interactions in receptor-G protein coupling

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Signaling

Background:

• Guanine nucleotide exchange in heterotrimeric G proteins, catalyzed by G protein-coupled receptors (GPCRs), is a fundamental signaling mechanism.
• While structural information on GPCRs and G proteins is available, the dynamic sequence of events during nucleotide exchange remains unclear.

Purpose of the Study:

• To elucidate the temporal sequence of interactions between the active GPCR rhodopsin (R*) and the holo-G protein during guanine nucleotide exchange.
• To investigate the role of specific binding sites and lipid modifications in mediating G protein-GPCR interactions.

Main Methods:

• Utilized time-resolved near-infrared light scattering to monitor interactions in native membranes.
• Employed mass-tagged peptides and G proteins to analyze binding site interactions.
• Investigated the impact of lipid modifications (myristoylation and farnesylation) on G protein binding.

Main Results:

• Binding of the Galpha and Ggamma C-terminal sites to R* is mutually exclusive.
• Interaction with R* necessitates at least one lipid modification on the G protein.
• A sequential binding model was proposed: initial Gbetagamma subunit interaction followed by Galpha C-terminal tail interaction to release GDP.

Conclusions:

• The G protein-GPCR interaction during nucleotide exchange is a sequential and transient process.
• Lipid modifications are essential for initiating the G protein interaction with the activated receptor.
• The findings provide a dynamic model for G protein activation initiated by GPCRs.