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The transmembrane domain of the amyloid precursor protein in microsomal membranes is on both sides shorter than

Beate Grziwa1, Marcus O W Grimm, Colin L Masters

  • 1Center for Molecular Biology Heidelberg, University of Heidelberg, INF 282, D-69120 Heidelberg, Germany. bgrziwa@ix.urz.uni-heidelberg.de

The Journal of Biological Chemistry
|November 28, 2002
PubMed

Insights

Researchers determined the transmembrane domain (TMD) length of C99, finding it shorter than predicted. This positions gamma-secretase cleavage sites within the membrane, supporting a model of intramembrane proteolysis.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Neuroscience

Background:

  • Amyloid precursor protein (APP) processing is crucial for understanding Alzheimer's disease.
  • Beta-amyloid-converting enzyme (BACE) and gamma-secretase cleave APP, generating fragments like C99.
  • The precise location and mechanism of gamma-secretase cleavage within the membrane remain debated.

Purpose of the Study:

  • To biochemically determine the transmembrane domain (TMD) length of C99.
  • To investigate the accessibility of gamma-secretase cleavage sites within the membrane.
  • To provide insights into the intramembrane proteolytic mechanism of gamma-secretase.

Main Methods:

  • Single cysteine mutagenesis scan of C99.
  • Cysteine modification using a membrane-impermeable labeling reagent.
  • Biochemical analysis in endoplasmic reticulum-derived microsomes.

Main Results:

  • The TMD of C99 was determined to be 12 residues long (residues 37-48), shorter than predicted.
  • Identified residues accessible to modification, indicating their location outside the membrane.
  • Gamma-secretase cleavage sites are positioned within the lipid bilayer, not accessible to cytosolic proteases.
  • The center of the TMD aligns with the gamma-cleavage site at residue 42.

Conclusions:

  • The TMD of C99 is shorter and positioned differently than previously predicted.
  • Gamma-secretase likely cleaves C99 within the membrane, consistent with intramembrane proteolysis.
  • These findings support a model where gamma-secretase is a membrane-bound enzyme acting at the center of the lipid bilayer.

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