EXT1
Exostosin-1 is a protein that in humans is encoded by the EXT1 gene.
This gene encodes one of the two endoplasmic reticulum-resident type II transmembrane glycosyltransferase – the other being EXT2 – which are involved in the chain elongation step of heparan sulfate biosynthesis. Mutations in this gene cause the type I form of multiple exostoses.
EXT1 is important for heparan sulfate biosynthesis; however, studies involving EXT1-deficient cell lines suggest that there is limited production of HS even in the absence of EXT1. These cells produced shorter HS chains than those with functional EXT1. The residual synthesis in EXT1-deficient cells occurred due to EXT2 or EXTL2 (EXT-like) enzymes, which proves their significant role in HS biosynthesis.