Abstract: Methods and systems for the discovery of high-affinity peptide ligands and the resulting compositions are described herein. The amino acid sequence of a target protein is used to identify one or more homologous proteins of the target protein. Publications and databases are textmined to retrieve the sequences of peptide ligands that bind to the homologues or the target protein. Complementary proteins, which are proteins that bind to the target or homologous proteins or to DNA, and their target protein- or DNA-binding regions may also be identified. These candidate ligands are predicted to have a high probability of binding to the target protein or the DNA. The library of candidate peptide ligands is modulated by substituting native amino acid residues with suitable amino acids, thus increasing the explored protein space in a knowledge-based manner.