Complementary peptides as antibody mimetics for protein purification and assay.

The possibility of designing sequence-directed recognition peptides (complementary peptides) able to noncovalently associate target peptides or proteins is one of the most important biotechnological applications deriving from the molecular recognition theory [MRT]. Complementary peptides can be used widely as synthetic ligands for the development of affinity purification strategies to isolate target peptides or proteins from crude sources. Generally, the observed affinity and selectivity are sufficient to allow one-step purification of target molecules directly from crude mixtures and the possibility of producing the ligands in enzymatically stable forms greatly enhance their applicability. In addition, the noninterference of nonionic detergents or denaturants on recognition expand their use in the case of poorly soluble targets. The ligand's synthetic nature overcomes all the problems associated with the use of immunoaffinity columns, since the possibility of biological contaminations is extremely limited. Numerous examples demonstrate the usefulness of this methodology, which allows the creation of a large number of peptidyl ligands tailored to specific purification needs. Recognition properties of complementary peptides can be applied also to the development of solid-phase assays for the identification and quantification of different molecular targets. As antibody mimetics, they can be used on solid phases to capture, and then to detect and consequently quantify, the desired target polypeptide in complex biological mixtures. Even if assay sensitivity cannot be compared with conventional antibody-based assays, the simplicity of complementary peptide design and production makes their use an attractive alternative in various circumstances.