6-O-sulfation enzyme which catalyzes the transfer of sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to position 6 of the N-sulfoglucosamine residue (GlcNS) of heparan sulfate. Critical for normal neuronal development where it may play a role in neuron branching. May also play a role in limb development. May prefer iduronic acid. {ECO:0000269|PubMed:21700882, ECO:0000269|PubMed:9535912}. This is the function of HS6ST1 (heparan sulfate 6-O-sulfotransferase 1, Ensembl gene identifier ENSG00000136720).