Stereo view of a crystal structure (1TB6) of the complex between antithrombin (purple), thrombin (blue), and a 16-mer heparin mimetic (SR123781A). The proteins are shown in cartoon with a semitransparent surface, and the oligosaccharide is represented as ball-and-stick, with carbon in green, oxygen in red, and sulfur in yellow. The oligosaccharide is composed of an antithrombin-specific pentasaccharide based on idraparanux, an uncharged seven-saccharide unit linker, and a highly sulfated four residue thrombin-binding unit. Picture courtesy of Jim Huntington, Professor of Molecular Haemostasis, University of Cambridge.