Physiological substrates for human lysosomal beta -hexosaminidase S.

Area of Science:

• Biochemistry
• Glycobiology
• Molecular Biology

Background:

• Human lysosomal beta-hexosaminidases (Hex A, Hex B, Hex S) degrade glycoconjugates.
• The physiological role of Hex S has been unclear despite its presence.

Purpose of the Study:

• To investigate the substrate specificity and physiological significance of Hex S.
• To identify the substrates responsible for the accumulation of oligosaccharides in Hex S-deficient mice.

Main Methods:

• Analysis of urinary oligosaccharides from double knockout mice using ESI-MS/MS and glycosidase digestion.
• In vitro enzymatic assays using recombinant Hex S with various substrates, including sulfated glycosphingolipid SM2.

Main Results:

• Hex S efficiently degrades sulfated glycosaminoglycan fragments and N-glycan degradation products.
• Recombinant Hex S shows high activity on artificial substrates, sulfated GAG fragments, and the sulfated glycosphingolipid SM2.
• Hex S activity on SM2 is enhanced by GM2 activator protein and bis(monoacylglycero)phosphate.

Conclusions:

• Hex S is physiologically significant for the degradation of dermatan sulfate and N-glycans.
• Hex S acts on specific sulfated glycoconjugates, including the glycosphingolipid SM2.
• The findings clarify the role of Hex S in lysosomal glycoconjugate degradation.