Description
FAM20B is a member of the FAM20 protein family that has three members in mammals (FAM20A, FAM20B, FAM20C). Human FAM20B shares 97% amino acid sequence identity with mouse and rat FAM20B. FAM20B localizes to the Golgi apparatus where it phosphorylates the xylose residue in the glycosaminoglycan (GAG)-protein linkage region of proteoglycans, which leads to enhanced GAG biosynthesis. Accordingly, chondroitin sulfate and heparan sulfate production is increased when FAM20B is over-expressed and reduced following FAM20B knockdown. FAM20B knockout mice display embryonic lethality at day E13.5, suggesting that FAM20B has an important role during development. Furthermore, in zebrafish, FAM20B mutations result in reduced cartilage matrix production and skeletal defects. The enzymatic activity of recombinant human FAM20B is measured using a phosphatase-coupled method