Primary structure of BACE1. BACE1 is a 501 amino acid Type-I transmembrane aspartic protease. The various subdomains of BACE1 are indicated by the lines to the right of the structure. Numbers refer to amino acid positions. The two signature aspartic protease active site motifs at positions 93 and 289 are shaded yellow. S--S denote positions of disulfide bridges within the catalytic domain; Ns represents positions of N-linked glycosylation sites; Rs indicates positions of acetylated arginine residues; Cs mark positions of S-palmitoylated cysteine residues; P indicates phosphorylation of serine 498; Ub denotes ubiquitination of lysine 501.