title: Contribution of Kunitz protease inhibitor and transmembrane domains to amyloid precursor protein homodimerization.
abstract: BACKGROUND
  The two major isoforms of the human amyloid precursor protein (APP) are APP695 and APP751. They differ by the insertion of a Kunitz-type protease inhibitor (KPI) sequence in the extracellular domain of APP751. APP-KPI isoforms are increased in Alzheimer's disease brains, and they could be associated with disease progression. Recent studies have shown that APP processing to Aβ is regulated by homodimerization, which involves both extracellular and juxtamembrane/transmembrane (JM/TM) regions.
  
  
  OBJECTIVE
  Our aim is to understand the mechanisms controlling APP dimerization and the contribution of the ectodomain and JM/TM regions to this process.
  
  
  METHODS
  We used bimolecular fluorescence complementation approaches coupled to fluorescence-activated cell sorting analysis to measure the dimerization level of different APP isoforms and APP C-terminal fragments (C99) mutated in their JM/TM region.
  
  
  RESULTS
  APP751 was found to form significantly more homodimers than APP695. Mutation of dimerization motifs in the TM domain of APP or C99 did not significantly affect fluorescence complementation.
  
  
  CONCLUSIONS
  These findings indicate that the KPI domain plays a major role in APP dimerization. They set the basis for further investigation of the relation between dimerization, metabolism and function of APP.
authors.affiliation: Institute of Neuroscience, Université Catholique de Louvain, Brussels, Belgium.
authors.forename: N
authors.initials: N
authors.lastname: Ben Khalifa
authors.forename: D
authors.initials: D
authors.lastname: Tyteca
authors.forename: P J
authors.initials: PJ
authors.lastname: Courtoy
authors.forename: J C
authors.initials: JC
authors.lastname: Renauld
authors.forename: S N
authors.initials: SN
authors.lastname: Constantinescu
authors.forename: J N
authors.initials: JN
authors.lastname: Octave
authors.forename: P
authors.initials: P
authors.lastname: Kienlen-Campard
mesh_terms: D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D019556:COS Cells; D002522:Chlorocebus aethiops; D019281:Dimerization; D005434:Flow Cytometry; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics; D009154:Mutation / Q000235:genetics; D011480:Protease Inhibitors / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization / Q000235:genetics / Q000502:physiology*; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D014162:Transfection
chemical_list: D016564:Amyloid beta-Protein Precursor; D001426:Bacterial Proteins; D008164:Luminescent Proteins; D011480:Protease Inhibitors; D020033:Protein Isoforms; C054562:yellow fluorescent protein, Bacteria