Schematic illustration of the HPPK•9 structure. Polypeptide chains are shown as a ribbon diagrams with helices (spirals) in cyan, strands (arrows) in orange, and loops (tubes) in grey. Compound 9 is shown as a stick model in atomic color scheme (C in grey, N in blue, O in red, and S in yellow) with electron density map (2Fo - Fc; contoured at 1.0 σ) as a blue net.