MUTATION OF ASPARTATE-82 OF THE HUMAN C5A RECEPTOR ABOLISHES THE SECRETORY RESPONSE TO HUMAN C5A IN TRANSFECTED RAT BASOPHILIC LEUKEMIA-CELLS

C5a is a potent chemoattractant for monocytes, neutrophils and other l eukocytes. The receptor for human C5a is a member of the rhodopsin sup erfamily of G protein-coupled receptors and contains an aspartate resi due (Asp(82)) within the putative second transmembrane domain conserve d in all other G protein-linked receptors. We investigated the role of this residue and also the carboxy-terminal 23 residues of the C5a rec eptor in ligand binding and signal transduction by expressing wild-typ e and mutant receptors in the rat basophilic leukemia cell line RBL-2H 3. Wild-type and truncated receptors coupled efficiently to effector s ystems, resulting in the C5a-dependent discharge of granule contents. In contrast RBL cells transfected with receptors in which Asp(82) had been mutated to asparagine did not respond to human C5a by secretion d espite binding human C5a with high affinity. We conclude therefore tha t Asp(82) is not involved in the interaction with ligand but is essent ial for the proper transduction of the ligand binding signal.