Structure of Cytokine Hydrophobic Cores

Diagrams were constructed that describe, using a common frame of reference, the interactions that occur within the hydrophobic cores of the left-handed four-helix bundles of interleukin-2, -4, -5, granulocyte/macrophage-, granulocyte-, macrophage-colony-stimulating factor, β- and γ-interferon, growth hormone, and leukemia inhibitory factor. Based on the assumption that the topologies of the ligand-receptor complexes are similar, analogous patterns were obtained from these diagrams and lead to the detailed comparison of the hydrophobic cores. These patterns were then used to obtain pairwise rigid-body superpositions among all of the four-helix bundles: values of the root-mean-square deviations (Cα-atoms) over the four α-helices of the bundles range from 1.14 Å to 3.22 Å. Two distinct groups are formed after clustering based on structural superposition of the ten cytokines.