Sulfotransferase that utilizes 3'-phospho-5'-adenylyl sulfate (PAPS) to catalyze the transfer of a sulfo group to an N-unsubstituted glucosamine linked to a 2-O-sulfo iduronic acid unit on heparan sulfate (PubMed:10520990, PubMed:10608887, PubMed:15304505, PubMed:9988768). Catalyzes the O-sulfation of glucosamine in IdoUA2S-GlcNS and also in IdoUA2S-GlcNH2 (PubMed:10520990, PubMed:15304505, PubMed:9988768). The substrate-specific O-sulfation generates an enzyme-modified heparan sulfate which acts as a binding receptor to Herpes simplex virus-1 (HSV-1) and permits its entry (PubMed:10520990). Unlike HS3ST1/3-OST-1, does not convert non-anticoagulant heparan sulfate to anticoagulant heparan sulfate (PubMed:10520990). {ECO:0000269|PubMed:10520990, ECO:0000269|PubMed:10608887, ECO:0000269|PubMed:15304505, ECO:0000269|PubMed:9988768}. This is the function of ENSG00000153976 (HS3ST3A1, heparan sulfate-glucosamine 3-sulfotransferase 3A1).