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. 2021 Jul 23;22(15):7888. doi: 10.3390/ijms22157888

Figure 1.

Figure 1

GAG catabolism begins with endohydrolysis of the polysaccharide chains to oligosaccharides. After this initial step, HS and DS oligosaccharides are degraded from their nonreducing ends (NRE) to monosaccharides and inorganic sulfate. The enzymes involved in the first two steps are IDS, which hydrolyzes the C2-sulfate ester bond of nonreducing terminal alpha-L-Iduronic acid (IdoA) residues in HS and DS and IDUA, which removes non-sulfated terminal alpha-L-IdoA residues. Under normal conditions, HS degradation produces IdoA and glucuronic acids (GlcA), while DS degradation results in IdoA and N-acetyl galactosamines (GalNAc). Defects in IDS activity result in accumulation of oligosaccharides with sulfated IdoA units on their NRE, while defects in IDUA activity result in oligosaccharides with non-sulfated IdoA units at their NRE [69].