Crystal structure of native PN1. (A) A stereo diagram representation of PN1 (monomer B) is shown in the classic orientation, with the RCL (yellow) on top and β-sheet A (red) facing. The missing N-terminal portion of the RCL is included for clarity, and the P1 arginine side chain is shown as sticks. Helix D is colored cyan, and the 3₁₀ helix C-terminal to helix D is green. Putative heparin-binding lysine side chains are shown to illustrate their distribution. (B) Native PN1 is colored as in panel A but oriented so that the heparin-binding site (helix D) is facing. (C) The surface electrostatic representation of PN1 is shown in the orientation of panel B (blue for positive and red for negative).