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. Author manuscript; available in PMC: 2013 Sep 13.
Published in final edited form as: Anal Chem. 2011 Sep 19;83(20):7815–7822. doi: 10.1021/ac201498a

Figure 4.

Figure 4

Structural complex of heparinase I with different GAG oligosaccharides. The active site of Hep I is shown as a cartoon representation (in gray) with the side chains of the key active site residues labeled. The basic residues Lys, His, and Arg are colored blue, and Tyr is colored orange. A trisaccharide motif comprising the cleavable hexosamine–uronic acid linkage is shown in stick representation colored by element (carbon in green for hexosamine and violet for uronic acid, oxygen in red and sulfur in yellow). The C5 proton of uronic acid is shown in white. (A) Demonstration of the critical interaction of H151 with the C-5 proton of iduronic acid in the heparin substrate (black dotted line). (B) In constrast, the C-5 proton of glucuronic acid is oriented such that it faces away from H151 and hence is not favorably positioned for abstraction. (C) The presence of a 3-O sulfate on uronic acid (red dotted circle) in persulfonated GAGs causes the plane of the H151 residue to change its orientation, making it unfavorable for abstraction of C-5 proton. (D) Consistent with observation in (B), the C-5 proton of the glucuronate in OSCS faces away from H151.