Figure 2: Structure of S100A10. A cartoon of the association of S100A10 with its two primary ligands, annexin A2 and plasminogen, is presented in 𝐴 . The figure illustrates the structure of S100A10 and the association of S100A10 with the amino-terminus of annexin A2 and with plasminogen. Each S100A10 monomer is composed of four α-helical domains H-I, H-II, H-III, and H-IV. Separating H-I and H-II helical regions is a loop, L1. The H-III and H-IV are separated by a second loop (L2). The H-II and H-III are connected by a flexible linker or hinge region (HR1). The points of interaction between the amino-terminus of annexin A2 and S100A10 are quite extensive and four hydrophobic amino acids of the amino terminus of annexin A2 (V3, I6, L7, and L10) form seven points of contact with helix H-I of one monomer, two points of contact with the hinge region, and nine points of contact with helix H-IV of the other monomer for a total of nineteen points of contact with S100A10. Shown also are the helical wheel projections for the S100A10-binding site for B, annexin A2; C, NS3; D, DLC1; E, TASK-1. The S100A10-binding region of these ligands consists of an amphipathic α-helix in which hydrophobic residues form a binding site on one side of the helix. The program for helical wheel projections was obtained from http://www.kael.net/helical.htm.