Heparan sulfate glucosamine 3-O-sulfotransferase 1, also known as HS3ST1, is sulfotransferase that utilizes 3'-phospho-5'-adenylyl sulfate (PAPS) to catalyze the transfer of a sulfo group to position 3 of glucosamine residues in heparan. This protein catalyzes the rate limiting step in the biosynthesis of heparan sulfate (HSact). This modification is a crucial step in the biosynthesis of anticoagulant heparan sulfate as it completes the structure of the antithrombin pentasaccharide binding site. Recombinant human HS3ST1 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.