Dimeric Transmembrane Orientations of APP/C99 Regulate γ-Secretase Processing Line Impacting Signaling and Oligomerization

Summary

Amyloid precursor protein (APP) cleavage by the β-secretase produces the C99 transmembrane (TM) protein, which contains three dimerization-inducing Gly-x-x-x-Gly motifs. We demonstrate that dimeric C99 TM orientations regulate the precise cleavage lines by γ-secretase. Of all possible dimeric orientations imposed by a coiled-coil to the C99 TM domain, the dimer containing the ³³Gly-x-x-x-Gly ³⁷ motif in the interface promoted the Aβ ₄₂ processing line and APP intracellular domain-dependent gene transcription, including the induction of BACE1 mRNA, enhancing amyloidogenic processing and signaling. Another orientation exhibiting the ²⁵Gly-x-x-x-Gly ²⁹ motif in the interface favored processing to Aβ _43/40. It induced significantly less gene transcription, while promoting formation of SDS-resistant “Aβ-like” oligomers, reminiscent of Aβ peptide oligomers. These required both Val24 of a pro-β motif and the ²⁵Gly-x-x-x-Gly ²⁹ interface. Thus, crossing angles imposed by precise dimeric orientations control γ-secretase initial cleavage at Aβ ₄₈ or Aβ _49, linking the former to enhanced signaling and Aβ ₄₂ production.

Graphical Abstract

Highlights

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  C99 dimeric transmembrane orientations regulate γ-secretase processing line

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  Aβ ₄₂ production and signaling are linked to the ³³Gly-x-x-x-Gly ³⁷ interface

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  SDS-resistant oligomers require the ²⁵Gly-x-x-x-Gly ²⁹ interface and a pro-β motif

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  C99 dimeric orientations impact its localization and processing by PSEN1 or PSEN2

Abstract

Biological Sciences; Biochemistry; Molecular Biology; Neuroscience