Table 1.

Representative peptides with a secondary structure and their biological activity.

Name	Sequence	Biological Activity	Secondary Structure	References
Calcitonin- Gene Related Peptide	ACDTATCVTHRLAGLLSRSGGVVKNNFVPTNVGSKAF	Vasodilator, Migrane	α-helix	[20]
Gramicidin S	cyclo[D-Phe-Pro-Val-Orn-Leu]2	Antimicrobial	Antiparallel β-sheet, cyclic	[21]
Peptide 2	KHQCHWECT-Cit-GRCRLVCGRSGS	Reacts with rheumatoid autoantibodies	β-hairpin, disulfide bonds (C4–C17, C8–C13)	[22]
DX600	GDYSHCSPLRYYPWWKCTYPDPEGGG	Inhibitor of angiotensin converting enzyme 2	Random coil, disulfide bond (C6–C17)	[23]

Unusual amino acids: Orn: Ornithine. Cit: Citrulline.