The present invention provides a method for producing modified stable
polypeptides introducing at least one non-natural amino acid into the
hydrophobic region of the polypeptide. The thermal and chemical stability
of such polypeptides is improved compared to those properties of its
corresponding wild type proteins.The invention further provides purified
leucine zipper and coiled-coil proteins in which the leucine residues
have been replaced with 5,5,5-trifluoroleucines, and the modified
proteins so produced demonstrate increased thermal and chemical stability
compared to their corresponding wild-type natural proteins.