Amino acid sequence presenting fusion polypeptide and its use

A method for producing an antibody specifically binding to a target antigen comprising the following steps:

• a) recovering from an experimental animal after the administration of a fusion polypeptide comprising a polypeptide according to formula I
• NH2—S2—X1—S1—COOH (formula I)
• wherein
• X1 comprises a random amino acid sequence or an amino acid sequence derived from a first polypeptide,
• S2 and S1 are non-overlapping amino acid sequences derived from a second polypeptide, and
• — denotes a peptide bond,
• wherein the second polypeptide is selected from the croup consisting of human FKBP12, Arabidopsis thaliana FKBP13, Thermus thermophilus SlyD, Escherichia coli SlyD and Thermococcus gammatolerans SlyD, and
• wherein X1 is inserted in place of the insert-in-flap-domain (IF-domain) of the second polypeptide;
• and
• wherein X1 is the amino acid sequence of the polypeptide B-cells that produce the antibody specifically binding to the amino acid sequence of X1, and
• b) cultivating a cell comprising a nucleic acid encoding the antibody specifically binding to the amino acid sequence of X1 and recovering the antibody from the cell or the cultivation medium and thereby producing an antibody specifically binding to a target antigen.