CHEMOKINE RECEPTOR-LIGAND INTERACTIONS MEASURED USING TIME-RESOLVED FLUORESCENCE

Two G protein-coupled receptor subtypes (CXCR1 and CXCR2) mediate Inte rleukin-8 (IL8) action in cells. A nonradioactive lanthanide-chelate d erivatized IL8 ligand was developed to measure the binding activity of the chemokine receptors, CXCR1 and CXCR2. Site-specific mutagenesis o f the carboxyl-terminal serine of IL8 to cysteine resulted in a mutant IL8 (IL8-S72C) having a single free sulfhydryl. Using an iodoacetamid e derivative of the Eu3+-chelate of N-(p-benzoic acid)diethylenetriami ne-N,N',N ''-tetraacetic acid (DTTA), incorporation of one Eu3+ per IL 8 molecule ([Eu3+]IL8-S72C) was achieved. The dissociation constant fo r this conjugate was similar to that measured for [I-125]IL8 (similar to 2 nM) when measured by time-resolved fluorometry using CHO cell lin es stably expressing CXCR1 or CXCR2 receptors. The sensitivity, stabil ity, and high specific activity of europium-labeled IL8 demonstrate th e usefulness of lanthanide-labeled proteins in the measurement of rece ptor-ligand interactions and may be extended to other peptide ligands.