THE MOLECULAR PATHOLOGY OF ACID MALTASE DEFICIENCY (AMD)

Project: Research project

Project Details

Description

Alpha-glucosidase deficiency (acid maltase deficiency-AMD) is a clinically
and biochemically heterogeneous lysosomal storage disease existing in a
generalized infantile and late-onset neuromuscular froms. Both clinical
states are characterized by a catalytically active microsomal
Alpha-glucosidase of unknown function. Studies of intracellular transport
of lysosomal hydrolases and evolving models of glycoprotein biosynthesis
suggest a dual role for the microsomal enzyme: as a biosynthetic precursor
of the lysosomal enzyme and as a glycoprotein-processing enzyme in the
post-translational assembly of macromolecular species. Recently two human
neutral Alpha-glucosidases, with diverse biochemical properties, have been
characterized and mapped to separate chromosomal loci distinct from the
lysosomal Alpha-glucosidase. Similarly, two microsomal "processing"
Alpha-glucosidases were subsequently identified and found to exhibit
partial catalytic overlap with the neutral Alpha-glucosidase activity. In
addition, we have identified a tissue-specific Alpha-glucosidase activity
in renal tissue, which has partial electrophoretic identity with the
lysosomal enzyme and is present in normal amounts in AMD renal samples. We
had previously demonstrated reduced levels of catalytically-active
lysosomal Alpha-glucosidase only in tissues from late-onset AMD patients,
while recent studies have shown reduced rates of synthesis of a
biosynthetic form of the lysosomal enzyme in these mutant cells, with lack
of immunoprecipitable material in the infantile AMD cells. The finding of
heterogeneous morphological alterations in AMD tissues coupled with the
evolving complexity of lysosomal enzyme biosynthesis and pathology
suggested to us that graded cellular alterations could occur as a
consequence of a selective mutant locus. As such, we conducted preliminary
studies which revealed major alterations in whole cell glycoprotein
biosynthesis and membrane assembly. We believe a program combining study
of glycoprotein biochemistry and molecular biology will best allow us to:
characterize the complex interrelationships between lysosomal and
microsomal Alpha-glucosidases, determine the molecular basis of functional
differences between infantile and late-onset AMD, and study the
consequences of a selective mutant locus on post-translational cellular
processing events. These studies will involve: comparative hydrolase
assays using putative natural saccharide substrates on purified neutral
Alpha-glucosidases, detailed structural analysis of glycoprotein
biosynthetic intermediates and mature membrane glycoproteins, in vitro
cell-free translation and biosynthetic labeling, and recombinant DNA
techniques. These studies are crucial to our understanding of molecular
mechanisms in lysosomal and general cellular pathology and to refinement in
techniques important to gene and enzyme replacement therapy in
neurodegenerative diseases.
StatusFinished
Effective start/end date12/1/8411/30/85

Funding

  • National Institute of Neurological Disorders and Stroke

ASJC

  • Molecular Medicine
  • Structural Biology
  • Biochemistry
  • Biotechnology
  • Cell Biology

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