Evolution of CAV ligands. Sequence alignment showing the progression of peptide ligands from the native gp41 segment sequence (2) to T20 (3), to ligands 4, 5, and 6, and ultimately to ligand 1, which binds CAV(1-104) with 7500-fold higher affinity despite an 80% decrease in length compared to 3. Residues mutated from 3 are in red. Numbers above 2 indicate the residue numbers from the original protein.