ANTIGENIC ANALYSIS OF THE 2ND EXTRA-CELLULAR LOOP OF THE HUMAN BETA-ADRENERGIC RECEPTORS

  • 1 October 1989
    • journal article
    • research article
    • Vol. 78  (1) , 42-48
Abstract
Polyclonal antibodies were raised in rabbits by immunization with free peptides corresponding to positions 197-222 of the human .beta.1-adrenergic receptor (.beta.1 peptide) and the corresponding sequence (172-197) of the human .beta.2-adrenergic receptor (.beta.2 peptide). While the .beta.2 peptide yielded antibodies that cross-reacted with the .beta.1 peptide, the antibodies against the .beta.1 peptide did not cross-react with the .beta.2 sequence. Cross-reactivity of the anti-.beta.2 peptide antibodies and the selectivity of the anti-.beta.1 peptide antibodies were also revealed in the recognition by immunoblots of the .beta.1- and .beta.2-adrenergic receptors of different species or of the receptor gene products expressed in a bacterial vector. These antibodies could be used immunohistochemically to visualize the .beta.-adrenergic receptors on rabbit heart. The anti-.beta.2 peptide antibodies did not show any functional effect on the .beta.-adrenergic receptors; the anti-.beta.1 peptide antibodies were able to displace agonist affinity to higher values. Recognition of truncated peptides by the anti-.beta.1 and anti-.beta.2 peptide antibodies suggested that the cross-reaction of the anti-.beta.2 peptide antibodies were due to the recognition of a common epitope on the C-terminal part of the peptides. The anti-.beta.1 peptide antibodies recognized the N-terminal part of the peptide better than the C-terminal part. These results suggest that the second extracellular loop postulated in the structure of the human .beta.-adrenergic receptor contains the T and B cell epitopes necessary for induction of an immune response. The selectivity and the functional properties of the antibodies raised against that loop in the .beta.1 adrenergic receptor could have relevance in induction of auto antibodies in certain cardiomyopathic conditions.