Figure 1.

The catalytic site of BACE-1 (1TQF structure). The Thr231 hydroxyl group located at a hydrogen bond distance from the Asp228 carboxyl moiety protects this group from protonation. A conserved water molecule (W2), forms three hydrogen bonds with residues Tyr71, Asn37 and Ser35, resulting in the formation of a continuous chain of hydrogen-bonded residues Trp76-Tyr71-W2-Ser35-Asp32 that connect the flap with the catalytic site. Hydrogen bonds are shown by dashed lines, amino acids are shown by sticks and water molecules are shown by red balls.