The crystal structures of the estrogen sulfotransferase and the sulfotransferase domain (NsT1) of human heparan sulfate NDST 1 (N-deacetylase/N-sulfotransferase) have been solved in the presence of 3'-phosphoadenosine 5'-phosphate (PAP) . These structures reveal structural similarity between sulfotransferase and nucleotide kinase.