FIGURE 3.

Stereo view of the 2F_o − F_c electron density around the side chain of R82, contoured at 1 σ. The side chain is shown in the two conformations that best account for difference density features that appeared during model building. Significant density remains in the F_o − F_c map if just the upward facing conformation and its corresponding waters are included in the atomic model. A second conformer was therefore modeled, with its accompanying waters, to account for the residual density features. Two of the most informative density features that are visible in this figure are the extended density accounted for by water molecules and the extra large density feature in which the guanidinium group of the arginine is located. In addition, only weak density is present for the side chain's three-carbon linker, further suggesting that this portion of the residue is highly mobile due to multiple conformations.