Patent ID: 7785903

Claim:
A polypeptide library comprising a plurality of monobody variable heavy chain domains, wherein each monobody variable heavy chain domain comprises a variant variable framework region (VFR), wherein the amino acid positions of the VFR form a loop in an antigen binding pocket, wherein the amino acid positions are according to the Kabat numbering system, wherein the VFR comprises: a) a N-terminal portion that comprises at least one structural amino acid position comprising one or both of the first two amino acid positions of the N-terminal portion of the VFR, wherein said structural amino acid position has a variant amino acid selected from the group consisting of up to six different amino acids, wherein the first amino acid position of the N-terminal portion corresponds to position 71 of a variable heavy chain domain and is C, F, Y, W, M, or L; b) a central portion that comprises at least one nonstructural amino acid position, wherein the nonstructural amino acid position has a variant amino acid comprising any of the naturally occurring amino acids; and c) a C-terminal portion that comprises at least one structural amino acid position, wherein said structural amino acid position has a variant amino acid selected from the group consisting of up to six different amino acids.