FIGURE 5.

KLK2 surface loops. A, stereo view of the 75-loop. The guanidinium group of Arg-70 interacts with putative calcium ligands, thereby precluding calcium binding. Hydrogen bonds are shown as black, dashed lines. B, the 148-loop is stabilized by hydrogen bonds that involve Ser-143 (cyan, dashed lines), Arg-151 (red, dashed lines), or backbone atoms only (black, dashed line). Maximum-likelihood 2mF_obs − DF_calc electron density contoured at 1.5σ is shown in blue for the side chains of arginines 70, 151, and 153.