Continuous spectrofluorometric analysis of formyl peptide receptor ternary complex interactions

Area of Science:

• Biochemistry
• Cellular Signaling
• Immunology

Background:

• Studying real-time ligand-receptor-G protein (ternary complex) dynamics is crucial for understanding cellular signaling.
• Limitations in flow cytometry hinder continuous observation of these complex interactions.

Purpose of the Study:

• To extend the analysis of ternary complex dynamics to the second time scale using a novel approach.
• To continuously observe ligand association and dissociation in the presence and absence of GTP[S].

Main Methods:

• Utilized fluorescently labeled N-formyl pentapeptide and quenched fluorescence upon receptor binding.
• Employed permeabilized neutrophils for extended observation of ternary complex dynamics.
• Analyzed ligand-receptor (LR) binary and ligand-receptor guanine nucleotide binding protein (LRG) ternary complex formation and dissociation.

Main Results:

• Observed comparable initial rates for LR and LRG complex formation.
• Found dissociation rates differing by two orders of magnitude.
• Demonstrated slow interconversions between LR and LRG in the absence of guanine nucleotide, with rapid decomposition at saturating GTP[S] levels.

Conclusions:

• The ternary complex model requires at least three sides for accurate fitting, improved by including precoupled receptor-G protein (RG) complexes.
• Subsecond assembly and disassembly of ternary complexes explain rapid cellular responses to formyl peptides.
• Analysis with subsaturating GTP[S] revealed coexisting LR and LRG classes and altered receptor coupling distributions.