Method for engineering immunoglobulins

Abstract

The present invention relates to a method for engineering an immunoglobulin comprising a variable domain and at least one modification in at least two structural loops of said immunoglobulin and determining the binding of said immunoglobulin to an epitope of an antigen, wherein the unmodified immunoglobulin does not significantly bind to said epitope, comprising the steps of: providing a nucleic acid encoding an immunoglobulin comprising at least two structural loops, modifying at least one nucleotide residue of each of said structural loops, transferring said modified nucleic acid in an expression system, expressing said modified immunoglobulin, contacting the expressed modified immunoglobulin with an epitope, and determining whether said modified immunoglobulin binds to said epitope, immunoglobulins produced by such a method and libraries of immunoglobulins.

What is claimed is: 
     
         1 . A library comprising at least 10 immunoglobulins with a modification in at least two structural loops, wherein said at least 10 immunoglobulins are obtainable by the a method for providing a polypeptide or an antigen binding fragment thereof, comprising an antibody variable domain having a modified structural loop region, wherein the modified structural loop region contributes to a non-CDR antigen binding site that specifically binds to a first epitope, wherein the unmodified structural loop region does not specifically bind to said first epitope, comprising the steps of:
 (a) providing a nucleic acid encoding an immunoglobulin or fragment thereof, comprising at least two structural loops of an antibody variable domain having an antigen binding site comprising CDR loops, wherein said antigen binding site comprising said CDR loops specifically binds a second epitope,   (b) performing a method of mutagenesis selected from the group consisting of random mutagenesis, semi-random mutagenesis and site-directed random mutagenesis of said structural loop, to modify at least three nucleotides of the nucleic acid of step (a), wherein the modification results in a substitution, deletion and/or insertion of three or more amino acids of said structural loops of the antibody variable domain of step (a),   
       wherein step (b) results in a structural loop region which comprises the at least one modified structural loop and which specifically binds to said first epitope, wherein said insertion does not comprise an insertion of a region selected from one or more of the group consisting of chimeric CDR-regions or CDR-like regions or canonical structures of CDR regions,
 (c) transferring said modified nucleic acid in an expression system, 
 (d) expressing said modified immunoglobulin, 
 (e) contacting the expressed modified immunoglobulin with an epitope, and 
 (f) determining whether said modified immunoglobulin retains the CDR binding site and further binds to said epitope.