Collagen XXV a1 (COL25A1), also known as CLAC-P and AMY, is an 80kD member of the transmembrane (TM) collagen family. It is type II TM hydroxylated glycoprotein that is expressed by neurons. Proteolytic cleavage generates 70kD monomers that either dimerizIgG2Be or trimerize, and bind to fibrillar amyloid b-peptide. Human COL25A1 is 654aa in length. It has a 600aa extracellular domain (aa55-654) that contains seven collagen-like regions and is cleaved by furin between Arg112 and Glu113. Multiple splice forms may exist. One shows a 5aa substitution for (aa441-654), while a second shows a 2aa substitution for (aa616-654). Three other isoforms show splicing over aa165-245 accompanied by complex splicing at the C-terminus. Over (aa189-654), human COL25A1 is 95% aa identical to mouse COL25A1.