title: Mechanism of intramembrane cleavage of alcadeins by γ-secretase.
abstract: BACKGROUND
  Alcadein proteins (Alcs; Alcα, Alcβand Alcγ) are predominantly expressed in neurons, as is Alzheimer's β-amyloid (Aβ) precursor protein (APP). Both Alcs and APP are cleaved by primary α- or β-secretase to generate membrane-associated C-terminal fragments (CTFs). Alc CTFs are further cleaved by γ-secretase to secrete p3-Alc peptide along with the release of intracellular domain fragment (Alc ICD) from the membrane. In the case of APP, APP CTFβ is initially cleaved at the ε-site to release the intracellular domain fragment (AICD) and consequently the γ-site is determined, by which Aβ generates. The initial ε-site is thought to define the final γ-site position, which determines whether Aβ40/43 or Aβ42 is generated. However, initial intracellular ε-cleavage sites of Alc CTF to generate Alc ICD and the molecular mechanism that final γ-site position is determined remains unclear in Alcs.
  
  
  METHODS
  Using HEK293 cells expressing Alcs plus presenilin 1 (PS1, a catalytic unit of γ-secretase) and the membrane fractions of these cells, the generation of p3-Alc possessing C-terminal γ-cleavage site and Alc ICD possessing N-terminal ε-cleavage site were analysed with MALDI-TOF/MS. We determined the initial ε-site position of all Alcα, Alcβ and Alcγ, and analyzed the relationship between the initially determined ε-site position and the final γ-cleavage position.
  
  
  CONCLUSIONS
  The initial ε-site position does not always determine the final γ-cleavage position in Alcs, which differed from APP. No additional γ-cleavage sites are generated from artificial/non-physiological positions of ε-cleavage for Alcs, while the artificial ε-cleavage positions can influence in selection of physiological γ-site positions. Because alteration of γ-secretase activity is thought to be a pathogenesis of sporadic Alzheimer's disease, Alcs are useful and sensitive substrate to detect the altered cleavage of substrates by γ-secretase, which may be induced by malfunction of γ-secretase itself or changes of membrane environment for enzymatic reaction.
authors: Laboratory of Neuroscience, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
authors: Yi
authors: Y
authors: Piao
authors: Ayano
authors: A
authors: Kimura
authors: Satomi
authors: S
authors: Urano
authors: Yuhki
authors: Y
authors: Saito
authors: Hidenori
authors: H
authors: Taru
authors: Tohru
authors: T
authors: Yamamoto
authors: Saori
authors: S
authors: Hata
authors: Toshiharu
authors: T
authors: Suzuki
mesh_terms: D020816:Amino Acid Motifs; D053829:Amyloid Precursor Protein Secretases / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000201:enzymology*; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010449:Peptide Mapping; D053764:Presenilin-1 / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D016229:Amyloid beta-Peptides; C503225:CLSTN1 protein, human; C472551:CLSTN2 protein, human; C472553:CLSTN3 protein, human; D002135:Calcium-Binding Proteins; D008565:Membrane Proteins; D010446:Peptide Fragments; D053764:Presenilin-1; D053829:Amyloid Precursor Protein Secretases
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