Abstract: The invention provides polypeptides comprising a variant heavy chain variable framework domain (VFR). In some embodiments, the amino acids defining the VFR form a loop of an antigen binding pocket. In an embodiment, the polypeptide is a variable domain of a monobody and has a variant VFR. The polypeptide may optionally comprise one or more complementary determining regions (CDRs) of antibody variable domains. In an embodiment, the polypeptide is a variable domain of a monobody and has a variant VFR and one or more variant CDRs. Libraries of polypeptides that include a plurality of different antibody variable domains generated by creating diversity in a VFR, and optionally, one or more CDRs are provided and may be used as a source for identifying novel antigen binding polypeptides that can be used therapeutically or as reagents. The invention also provides fusion polypeptides, compositions, and methods for generating and using the polypeptides and libraries.

Abstract: The invention provides immunoglobulin polypeptides comprising variant amino acids in CDRs of antibody variable domains. In one embodiment, the polypeptide is a variable domain of a monobody and has a variant CDRH3 region. These polypeptides provide a source of great sequence diversity that can be used as a source for identifying novel antigen binding polypeptides. The invention also provides these polypeptides as fusion polypeptides to heterologous polypeptides such as at least a portion of phage or viral coat proteins, tags and linkers. Libraries comprising a plurality of these polypeptides are also provided. In addition, methods of and compositions for generating and using these polypeptides and libraries are provided.