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Structural and mechanistic insight into the basis of mucopolysaccharidosis IIIB

Elizabeth Ficko-Blean1, Keith A Stubbs, Oksana Nemirovsky

  • 1Department of Biochemistry and Microbiology, University of Victoria, P.O. Box 3055, Station CSC, Victoria, BC, Canada.

Proceedings of the National Academy of Sciences of the United States of America
|April 30, 2008
PubMed

Insights

Mucopolysaccharidosis III type B (MPS IIIB) results from low alpha-N-acetylglucosaminidase (NAGLU) activity. Studying a bacterial homolog revealed enzyme structure, aiding MPS IIIB genetic insights and potential chemical chaperone drug design.

Area of Science:

  • Biochemistry
  • Structural Biology
  • Genetics

Background:

  • Mucopolysaccharidosis III (MPS III) encompasses four forms (A-D), each caused by the accumulation of undegraded glycosaminoglycans within lysosomes.
  • MPS IIIB specifically arises from deficient activity of the lysosomal enzyme alpha-N-acetylglucosaminidase (NAGLU).
  • Despite over two decades of research, the structure of human NAGLU has remained elusive, hindering detailed mechanistic and therapeutic studies.

Purpose of the Study:

  • To elucidate the structure, catalytic mechanism, and inhibition of CpGH89, a bacterial homolog of NAGLU.
  • To generate a reliable homology model of human NAGLU based on the CpGH89 structure.
  • To identify potential small-molecule inhibitors of CpGH89 as candidates for chemical chaperones to treat MPS IIIB.

Main Methods:

  • X-ray crystallography was used to determine the structure of CpGH89 from Clostridium perfringens.
  • Homology modeling was employed to create a structural model of human NAGLU.
  • Enzyme inhibition assays and co-crystallization studies were performed to analyze inhibitor binding.

Main Results:

  • The determined structure of CpGH89 provided insights into its catalytic mechanism.
  • A homology model of NAGLU was successfully generated, revealing the active site and mutation locations for MPS IIIB.
  • Potent inhibitors of CpGH89 were identified, and their complexes with the enzyme were structurally characterized.

Conclusions:

  • The structural and mechanistic studies of CpGH89 illuminate the genetic basis of MPS IIIB.
  • The findings provide a biochemical rationale for the sequential action of heparan-degrading enzymes.
  • This work paves the way for designing and optimizing chemical chaperones for MPS IIIB treatment.

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