Fig. 1.

The antithrombin-binding motif (ABM) in heparin/heparan sulfate (Hp/HS) is introduced by 3-O-sulfotransferase isoform 1 (3OST-1; also called HS3ST-1) when it acts on the precursor sequence to convert the 3-OH group of central GlcN residue (red) to the 3-O-sulfate group (OSO₃⁻). In this work, the precursor sequence residues are labeled as −2, −1, 0, +1, +2 residues (red labels), where the site of 3-O-sulfation by 3OST-1, identified as the 0th residue, is the centerpiece of biosynthetic modification. X can be SO₃⁻ or COCH₃ and Y can be H or SO₃⁻. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)