Statistical analyses of the 145 BACE1 data sets deposited in the PDB. (a) Hydrogen-bond (red) and hydrophobic (green) interactions between ligands and amino-acid residues in the 208 different BACE1 complex structures. The numbers of hydrogen-bond and hydrophobic interactions were assessed using LIGPLOT. (b) R.m.s.f. values for the main-chain atoms of the individual amino-acid residues in BACE1 calculated on the basis of the 222 available apo and complex structures extracted from the 145 BACE1 data sets. (c) The minimal distance between the Cα atoms of flap residues 67–75 and the two carboxyl O atoms of Asp228 in the 208 complex (black) and 14 apo (red) conformations of BACE1. The structures are grouped according to the space groups to which they belong.