title: Characterisation of C5a receptor agonists from phage display libraries.
abstract: C5a des-Arg(74) has a 10- to 100-fold lower receptor binding affinity than intact C5a and is only a partial agonist. We have used phage display selection from randomly mutated C5a des-Arg(74) libraries to isolate variant proteins that can activate C5a receptors with similar potency to C5a. Here we explore the interactions of three variants (V1-3) with C5aR mutated at residues involved in the differential response. The mutant Asp(282)Arg-C5aR is preferentially activated by C5a des-Arg(74), probably due to repulsion between Arg(74) of C5a and the substituent Arg(282). In accordance with this hypothesis, V2 (with a polar C-terminus which has no Arg residue) but not V1 (with a C-terminal Arg residue at position 73) could activate Asp(282)Arg-C5aR. V3, with a very hydrophobic C-terminus, was the most potent agonist at Asp(282)Arg-C5aR. Arg(175) is a potential counterion for the C-terminal carboxylate of C5a. C5aR mutated to either Ala or Asp at this position lost nearly all responsiveness to both C5a and C5a des-Arg(74), suggesting that mutation of Arg(175) caused a non-specific loss of receptor conformation and a loss of signalling capacity. However, V3 could still activate Arg(175)Asp/Ala-C5aR with the same potency as wild-type C5aR, demonstrating that the mutant receptors retained high signalling capability and showed a specific loss of responsiveness. Thus C5a des-Arg(74) variants produced by phage display are potentially useful tools for the dissection of ligand-receptor interactions.
authors.affiliation: Academic Neurology Unit, University of Sheffield Medical School, Sheffield S10 2RX, UK.
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Cain
authors.forename: Adrian
authors.initials: A
authors.lastname: Higginbottom
authors.forename: Peter N
authors.initials: PN
authors.lastname: Monk
mesh_terms: D000818:Animals; D015937:Complement C5a, des-Arginine / Q000235:genetics / Q000494:pharmacology*; D019151:Peptide Library; D051381:Rats; D044087:Receptor, Anaphylatoxin C5a / Q000819:agonists*; D011971:Receptors, Immunologic / Q000819:agonists; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D015937:Complement C5a, des-Arginine; D019151:Peptide Library; D044087:Receptor, Anaphylatoxin C5a; D011971:Receptors, Immunologic