a disadvantage for potential drugs. Production Molecular libraries of Affilin proteins are generated by randomizing sets of amino acids by mutagenesis methods. Substituting selected amino acids at the potential binding site gives 198 ≈ 17,000,000,000 possible combinations (e.g.: eight amino acids substituted by 19 amino acids). Cysteine is excluded because of its liability to form disulfide bonds. In an Affilin protein comprising two modified ubiquitin molecules, for example, up to 14 amino acids are exchanged, resulting in 8 × 1017 combinations, but not all of these are realized in a given library. The next step is the selection of Affilin proteins that bind the desired target protein. To this end display techniques such as phage display or ribosome display are used. The fitting species are isolated and characterized physically, chemically and pharmacologically. Subsequent dimerisation or multimerisation can increase plasma half-life and, due to avidity, affinity to the target protein. Alternatively, multispecific Affilin molecules can be generated, binding different targets simultaneously. Radionuclides or cytotoxins can be conjugated to Affilin proteins, making them potential tumour therapeutics and diagnostics. Conjugation of cytokines has also been tested in vitro. Large-scale production of Affilin proteins is facilitated by E. coli and other organisms commonly used in biotechnology. References External links Scil Proteins, the developer Antibody mimetics