Interleukin 2

The Interleukin 2 (IL-2) family of cytokines plays a critical role in the functioning of the immune system including the modulation of lymphocyte activities. This family of cytokines includes IL-2, IL-4, IL-7, IL-9 and IL-15, each of which shares the IL-2 receptor γ chain (IL-2Rγ). Due to its shared nature, IL-2Rγ is known as the common cytokine receptor γ chain (γc). In addition to γc, the receptor for each of the IL-2 family cytokines contains at least one other component, such as IL-2Rβ, IL-4Rα, IL-7Rα and IL-9Rα, which contributes both to binding and to transduction of specific signals. Additionally, because the receptors for IL-2 and IL-15 share IL-2Rβ, IL-2 and IL-15 have the most overlapping biological activities of the five cytokines.

Figure This is a crystal structure of human IL-2 as published by Arkin et al.  and created using the data from Protein Data Bank (PDB: 1M47) and rendered using PyMOL.

IL-2 is a cytokine that induces proliferation of responsive T cells. In addition, it acts on some B cells, via receptor-specific binding, as a growth factor and stimulates antibody production. The protein is secreted as a single glycosylated polypeptide, and cleavage of a signal sequence is required for activity. Solution NMR suggests that the structure of IL-2 consists of a bundle of 4 helices (termed A-D), flanked by shorter helices and several poorly defined loops. Residues in helix A, and in the loop region between helices A and B, are important for receptor binding. Secondary structure analysis has suggested similarity to IL-4 and granulocyte-macrophage colony stimulating factor (GM-CSF).