Alignment of the mature enzyme regions of PxAP8 and PxAP9 predicted polypeptides with human BACE (Hs_BACE1) and BACE2 (Hs_BACE2). The numbering system is that of pig pepsin. The DT/SG and hydrophobic-hydrophobic-Gly motifs forming the psi loops in each domain are boxed. Landmark residues 75 and 39 are boxed as in previous figures, but here to emphasise the Y75F and W39A replacements (highlighted black). Residue 80 is also boxed to indicate the presence of a W residue at this location in PxAP8 and BACE/BACE2. The Cys residues contributing the three disulphide bonds in BACE are shaded and their known pairing is indicated by thick () and dotted black lines ().