Cartoons view of Interleukin-4, a 4-helix bundle in blue, with its receptor in green.
At the interface, Arg and Lys are colored blue, Asp and Glu are colored red, polar residues are colored yellow, and nonpolar residues are colored gray.
Everything shown in spacefilling.
Notice the pattern of red and blue, and the patches of yellow and gray.
1iar (PDB)
Hage, T., Sebald, W., Reinemer, P.: Crystal Structure of the Interleukin-4 / Receptor Alpha Chain Complex Reveals a Mosaic Binding Interface Cell (Cambridge,Mass.) 97 pp. 271 (1999) (PubMed)