AN AGONIST-LIKE MONOCLONAL-ANTIBODY AGAINST THE HUMAN BETA(2)-ADRENOCEPTOR

Monoclonal antibodies were produced against a peptide corresponding to the second extracellular loop of the human beta(2)-adrenoceptor. One of these monoclonals, inducing an agonist-like effect in neonatal rat cardiomyocytes, was used to define the structural and physiological ba sis of this activity. The epitope recognized by the antibody correspon ds to the sequence Trp-Tyr-Arg-Ala-Thr-His-Gln-Glu as determined by pe ptide scanning. Analysis by alanine modification of the peptide epitop e showed the importance of the Trp, and Glu residues in antibody recog nition The apparent affinity of the antibody assessed either by surfac e plasmon resonance or by functional titration on its agonist-like act ivity showed a similar value (108 M-l). The antibody recognized the re ceptor in its native form as shown by immunofluorescence experiments o n A431 cells but not in its denatured form as shown by its absence of staining in immunoblots. The positive chronotropic effect in vitro was specifically blocked by both the antigenic peptide and the specific i nden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride (ICI11 8,551). This activity was mediated through activation of Ca2+ L-type c hannels as assessed in guinea pig cardiomyocytes, These results sugges t that the epitope is located in an extracellular alpha-helix, whose r ecognition by the antibody could stabilize the receptor in its 'active ' conformation. (C) 1998 Elsevier Science B.V.