Three States for the Formyl Peptide Receptor on Intact Cells

Abstract Three distinct states of the formyl peptide receptor have been described. These are: 1) the ternary complex of ligand, receptor, and G protein (LRG); 2) the rapidly dissociating occupied receptor (ligand-receptor complex (LR]; and 3) a desensitized slowly dissociating guanine nucleotide-insensitive receptor (desensitized ligand-receptor complex ("LRX"]. During cell activation there is a rapid interconversion among receptor states from a rapidly dissociating form (t 1/2 approximately 10 s) to a slowly dissociating form (t 1/2 greater than or equal to 2 min). Neither the dynamics of the states nor their interconversion is influenced by ribosylation of G protein in the presence of pertussis toxin. In contrast to ribosylation, treatment of cells with either 2-deoxyglucose or fluoride ion, both of which lead to a loss of adenine and guanine nucleotides, causes a time-dependent change in ligand dissociability. After short periods of treatment (5-15 min) rapid dissociation is observed; after longer times (30-60 min), slow dissociation is once again detected. When intact cells are first ribosylated and then energy-depleted, only a rapidly dissociating receptor is detected. These results are discussed in terms of a model with the following elements: 1) intact cell dynamics during cell activation are dominated by an energy-dependent interconversion from LR to LRX; 2) under activation conditions, LRG appears and disappears too rapidly to be detected; 3) in cells depleted of energy and guanine nucleotide, LRG is stabilized; 4) in cells both ribosylated and depleted of energy, LR is stabilized.