Melanoma Associated ME20 (ME20M)

PMEL is a 100 kDa type I transmembrane glycoprotein that is expressed primarily in pigment cells of the skin and eye. The transmembrane form of PMEL is modified in the secretory pathway by elaboration of N-linked oligosaccharides and addition and modification of O-linked oligosaccharides. Some of these fragments form non-pathological amyloid that assemble into sheets and form the striated pattern that underlies melanosomal ultrastructure. PMEL cleavage is mediated by several proteases including a proprotein convertase of the furin family, a "sheddase" that might include members of the a disintegrin and metalloproteinase (ADAM) family, and additional proteases in melanosomes or their precursors. After the amyloidogenic region is cleaved, the small remaining integral membrane fragment is digested by γ-secretase.