Arginine 206 of the C5a Receptor Is Critical for Ligand Recognition and Receptor Activation by C-terminal Hexapeptide Analogs (∗)

• Published in: The Journal of biological chemistry Vol. 270; no. 27; pp. 15966 - 15969
• Main Authors: DeMartino, Julie A., Konteatis, Zenon D., Siciliano, Salvatore J., Van Riper, Gail, Underwood, Dennis J., Fischer, Paul A., Springer, Martin S.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 07.07.1995; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Sequence; Antigens, CD - chemistry; Antigens, CD - genetics; Arginine - genetics; Binding Sites; Complement C5a - chemistry; Dose-Response Relationship, Drug; Humans; Ligands; Models, Biological; Molecular Sequence Data; Mutation; Oligopeptides - pharmacology; Receptor, Anaphylatoxin C5a; Receptors, Complement - chemistry; Receptors, Complement - genetics; Signal Transduction; Structure-Activity Relationship
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.270.27.15966

C5a is a 74-amino-acid glycoprotein whose receptor is a member of the rhodopsin superfamily. While antagonists have been generated to many of these receptors, similar efforts directed at family members whose natural ligands are proteins have met with little success. The recent development of hexapeptide analogs of C5a has allowed us to begin elucidation of the molecular events that lead to activation by combining a structure/activity study of the ligand with receptor mutagenesis. Removal of the hexapeptide's C-terminal arginine reduces affinity by 100-fold and eliminates the ability of the ligand to activate the receptor. Both the guanidino side chain and the free carboxyl of the arginine participate in the interaction. The guanidino group makes the energy-yielding contact with the receptor, while the free carboxylate negates “electrostatic” interference with Arg-206 of the receptor. It is the apparent movement Arg-206 induced by this set of interactions that is responsible for activation, since conversion of Arg-206 to alanine eliminates the agonist activity of the hexapeptides. Surprisingly, activation is a nearly energy-neutral event and may reflect the binding process rather than the final resting site of the ligand.