Cysteine noose specific binding members and antibody libraries

The antibody libraries comprise a repertoire of at least 103 specific binding members comprising an antibody variable domain each carrying a cysteine noose in at least one of their CDRs, preferably CDR3 of a V-H domain. The repertoire is useful in the selection of specific binding members capable of binding a target antigen and in the obtention of peptide ligand mimetics. Also provided are specific binding members comprising a variable domain, such domain carrying a cysteine noose in at least one CDR and wherein (i) when said CDR is CDR3/V-H then the noose comprises other than 0,1,3,4 or 8 amino acids between the cys residues or (ii) said binding member is capable of binding to a cancer antigen (other than CEA when the noose is present in CDR3/V-H), a viral antigen or receptor, a hormone or hormone receptor, a cytokine or cytokine receptor or a growth factor or growth factor receptor.