IL17A/F

The IL-17 family comprises IL17A, IL-17B, IL-17C, IL-17D, IL-17E and IL-17F. IL-17E is also known as IL-25. All members of the IL-17 family have a similar protein structure. Their protein sequences contain four highly conserved cysteine residues. These conserved cysteine residues are critical to the right 3-dimensional shape of the entire protein molecule. To the reference, the members of IL-17 family do not exhibit a significant sequence homology with other cytokines. Among IL-17 family members, the IL-17F isoforms 1 and 2 (ML-1) have the highest sequence homology with IL-17A (55 and 40%, respectively). They follow by IL-17B, which has 29% similarity to IL-17A, IL-17D (25%), IL-17C (23%), and IL-17E (17%). In mammals, the sequences of these cytokines are highly conserved. For instance, the sequence homology between the corresponding human and mouse proteins is usually between 62–88%.