Figure 4.

The Trp41 rotamer and Trp41-Asp44 contact in the (A) high pH, drug-bound solution NMR structure (2RLF), and (B) the pH 6.5 X-ray crystal structure (3LBW). A larger pore radius at Trp41 is found in B due to the 180° χ₂ angle change. The Trp41 side chains are shown in spheres for Trp41 (green for C, blue for N), and in ball-and-stick for Asp44 (pink C, blue O). His37 is shown as spheres with orange for C, blue for N. His37′s side chain is almost fully occluded by Trp41 in (A); in (B), it has slightly more accessibility. Crystallographically defined water molecules are shown in small red spheres in B, with hydrogen bonds shown in dashed lines.