Norrin: Proteins and Enzymes

Norrin (also called Norrie Disease Protein or NDP) is a secreted regulatory protein, mutations in which cause Norrie disease (X-linked retinal dysplasia). Norrin consists of disulfide-linked homodimers that oligomerize further via disulfide bridges to form higher order oligomers containing up to ten units of 12 kDa each. Molecular modeling studies predict that Norrin assumes a cysteine-knot structure typical for the TGF-beta family. Although Norrin is not related to Wnt family proteins, it functions like a Wnt protein in that it binds with high affinity to the receptor Frizzled-4, requires LDL receptor-related protein (LRP) as a co-receptor, and induces activation of the canonical Wnt signaling pathway.