title: The backbone dynamics of the amyloid precursor protein transmembrane helix provides a rationale for the sequential cleavage mechanism of γ-secretase.
abstract: The etiology of Alzheimer's disease depends on the relative abundance of different amyloid-β (Aβ) peptide species. These peptides are produced by sequential proteolytic cleavage within the transmembrane helix of the 99 residue C-terminal fragment of the amyloid precursor protein (C99) by the intramembrane protease γ-secretase. Intramembrane proteolysis is thought to require local unfolding of the substrate helix, which has been proposed to be cleaved as a homodimer. Here, we investigated the backbone dynamics of the substrate helix. Amide exchange experiments of monomeric recombinant C99 and of synthetic transmembrane domain peptides reveal that the N-terminal Gly-rich homodimerization domain exchanges much faster than the C-terminal cleavage region. MD simulations corroborate the differential backbone dynamics, indicate a bending motion at a diglycine motif connecting dimerization and cleavage regions, and detect significantly different H-bond stabilities at the initial cleavage sites. Our results are consistent with the following hypotheses about cleavage of the substrate: First, the GlyGly hinge may precisely position the substrate within γ-secretase such that its catalytic center must start proteolysis at the known initial cleavage sites. Second, the ratio of cleavage products formed by subsequent sequential proteolysis could be influenced by differential extents of solvation and by the stabilities of H-bonds at alternate initial sites. Third, the flexibility of the Gly-rich domain may facilitate substrate movement within the enzyme during sequential proteolysis. Fourth, dimerization may affect substrate processing by decreasing the dynamics of the dimerization region and by increasing that of the C-terminal part of the cleavage region.
authors.affiliation: Lehrstuhl Chemie der Biopolymere, Technische Universität München, Weihenstephaner Berg 3, and Munich Center For Integrated Protein Science (CIPSM), 85354 Freising, Germany.
authors.forename: Oxana
authors.initials: O
authors.lastname: Pester
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Barrett
authors.forename: Daniel
authors.initials: D
authors.lastname: Hornburg
authors.forename: Philipp
authors.initials: P
authors.lastname: Hornburg
authors.forename: Rasmus
authors.initials: R
authors.lastname: Pröbstle
authors.forename: Simon
authors.initials: S
authors.lastname: Widmaier
authors.forename: Christoph
authors.initials: C
authors.lastname: Kutzner
authors.forename: Milena
authors.initials: M
authors.lastname: Dürrbaum
authors.forename: Aphrodite
authors.initials: A
authors.lastname: Kapurniotu
authors.forename: Charles R
authors.initials: CR
authors.lastname: Sanders
authors.forename: Christina
authors.initials: C
authors.lastname: Scharnagl
authors.forename: Dieter
authors.initials: D
authors.lastname: Langosch
mesh_terms: D053829:Amyloid Precursor Protein Secretases / Q000737:chemistry / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D013816:Thermodynamics
chemical_list: D016229:Amyloid beta-Peptides; D053829:Amyloid Precursor Protein Secretases