Figure 2 - full size

 

Figure 2.
Figure 2 Schematic drawing of interactions and distances around the active site determined from the crystal structure of BCA II at pH 7.5. The net charges assigned by theoretical calculations using MOPAC are shown. The side-chain atom Gln91 O 1 (net charge -0.30) accepts a hydrogen bond from of His93 N 1 (net charge -0.21) and contributes to His93 ligand stabilization. The side-chain atom of Gln91 N 2, with a net charge of -0.40, has a dominant role in the binding of water molecule W482, with net charge of +0.02, in its slightly acidic or cationic form. This interaction is likely to be more hydrogen-bonding in character than the interaction between W162 (net charge +0.01) and His63 N 2 (net charge -0.14) that has been a biological focus in the case of HCA II. This finding suggests that the dipole donor group of Gln91 may also participate in processes that require relatively rapid proton movement or release.

The above figure is reprinted by permission from the IUCr: Acta Crystallogr D Biol Crystallogr (2004, 60, 792-795) copyright 2004.