The present invention relates to novel β-AR homologous cyclopeptide-mutants comprising only two cysteine residues able to form an intramolecular linkage, to linear peptides that can form these cyclopeptide-mutants and to nucleic acid molecules encoding these cyclopeptide-mutants and linear peptides. Moreover, vectors and recombinant host cells comprising said nucleic acid molecule and a method for producing the disclosed cyclopeptide-mutants are provided. Further provided is a composition comprising the peptides, nucleic acid molecules, vectors or host cells of the invention. The present invention also relates to therapeutic and diagnostic means, methods and uses taking advantage of the peptides of the invention and to means, methods and uses for detecting anti-β-adrenergic receptor antibodies like anti-β1-adrenergic receptor antibodies.
