Amino Acid Substitution
The replacement of one amino acid with another at a specific position in a peptide sequence. Amino acid substitutions are a primary strategy in peptide drug design, used to improve receptor binding, resist enzymatic degradation, or alter pharmacokinetic properties while maintaining the core biological activity.
Technical Context
Strategic substitutions serve multiple purposes in peptide drug design. Replacing L-amino acids with D-amino acids at protease-susceptible sites confers resistance to enzymatic cleavage. Substitution with alpha-aminoisobutyric acid (Aib, a non-natural amino acid) at position 8 of GLP-1 analogues prevents DPP-4 cleavage — this modification is used in semaglutide and other GLP-1 RAs. Conservative substitutions (replacing amino acids with chemically similar alternatives) can fine-tune receptor binding affinity and selectivity. Non-conservative substitutions may create entirely new pharmacological profiles. Structure-activity relationship (SAR) studies systematically evaluate how each position in the sequence contributes to biological activity.