Characterization of APH-1 mutants with a disrupted transmembrane GxxxG motif

J Mol Neurosci. 2006;29(1):35-43. doi: 10.1385/JMN:29:1:35.


APH-1 is one of the four essential components of presenilin (PS)-gamma-secretase complexes. There are three major isoforms of APH-1 in humans: APH-1aS, APH-1aL, and APH-1b. To gain insight into the functional role of APH-1 in gamma-secretase complexes, we analyzed the relationship between the three APH-1 forms and characterized APH-1 mutants with a disrupted transmembrane GxxxG motif. We found that overexpression of APH-1aS or APH-1b in human cells significantly reduced the levels of endogenous APH-1aL protein. However, this displacement was not observed in PS-deficient cells, suggesting that it is dependent on PS. In transiently transfected cells, the levels of APH-1aL with G122D or L123D mutations were much lower than wild-type APH-1aL. Also, cycloheximide treatment of stable transfectants revealed that the mutant proteins are much less stable than the wild type. Furthermore, coimmunoprecipitation analysis showed that wild-type but not the mutant APH-1aL is incorporated into PS1 complexes, displacing endogenous APH-1aS. These results collectively indicate that the three forms of APH-1 can replace each other in PS complexes and that the transmembrane GxxxG region is essential for the stability of the APH-1 protein as well as the assembly of PS complexes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence*
  • Animals
  • Cell Line
  • Cycloheximide / metabolism
  • Endopeptidases
  • Humans
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics*
  • Membrane Proteins / metabolism
  • Mutation*
  • Peptide Hydrolases
  • Protein Isoforms / chemistry
  • Protein Isoforms / genetics*
  • Protein Isoforms / metabolism
  • Protein Structure, Secondary
  • Protein Synthesis Inhibitors / metabolism


  • Membrane Proteins
  • Protein Isoforms
  • Protein Synthesis Inhibitors
  • Cycloheximide
  • APH1A protein, human
  • Endopeptidases
  • Peptide Hydrolases