GxxxG motifs within the amyloid precursor protein transmembrane sequence are critical for the etiology of Aβ42

Abstract

Processing of the amyloid precursor protein (APP) by b-and c-secretases leads to the generation of amyloid-b (Ab) peptides with varying lengths. Particularly Ab42 contributes to cytotoxicity and amyloid accumulation in Alzheimer's disease (AD). However, the precise molecular mechanism of Ab42 generation has remained unclear. Here, we show that an amino-acid motif GxxxG within the APP transmembrane sequence (TMS) has regulatory impact on the Ab species produced. In a neuronal cell system, mutations of glycine residues G29 and G33 of the GxxxG motif gradually attenuate the TMS dimerization strength, specifically reduce the formation of Ab42, leave the level of Ab40 unaffected, but increase Ab38 and shorter Ab species. We show that glycine residues G29 and G33 are part of a dimerization site within the TMS, but do not impair oligomerization of the APP ectodomain. We conclude that c-secretase cleavages of APP are intimately linked to the dimerization strength of the substrate TMS. The results demonstrate that dimerization of APP TMS is a risk factor for AD due to facilitating Ab42 production.

Amyloid beta 42 peptide (Aβ42)-lowering compounds directly bind to Aβ and interfere with amyloid precursor protein (APP) transmembrane dimerization

“…In this respect, the effects of 20 μM indomethacin and 2.5 μM sulindac sulfide can be directly compared to GxxxG mutants G29A and G33A (5,7). From previous NMR measurements with purified and monodisperse C99 in lyso-myristoylphosphatidylglycerol micelles, the authors have concluded that interactions with sulindac sulfide are of nonspecific nature (15), which is seemingly in contradiction with our results obtained from the ToxR assay.…”

“…For analyzing the ability of selected compounds to affect APP-TMS dimerization, we applied the well-established ToxR system using the APP-TMS residues 29-42 according to Aβ numbering ( Fig. 4A) (5,16). Briefly, this assay allows monitoring of homophilic interactions of short α-helical TMSs in bacterial membranes, as dimerization of the TMS under study is required for transcription activation of the reporter gene β-galactosidase (β-Gal) (16).…”

“…β-CTF is the only known γ-secretase substrate comprising a GxxxG motif in triplicate, thus making dimerization of the APP-TMS unique (6). Mutational analysis revealed that a disruption of the dimer interface by glycine to alanine mutations at positions 29 and 33 of the Aβ sequence gradually attenuated the TMS-dimerization strength and diminished the formation of Aβ42 in favor of Aβ38, whereas Aβ40 levels remained largely unaffected (5). In addition, a subset of nonsteroidal antiinflammatory drugs (NSAIDs), including indomethacin and sulindac sulfide, effectively modulate the production of Aβ peptides in vitro and in vivo (7).…”

“…Previous attempts to understand γ-secretase cleavage specificity have unraveled that processing of the APP C-terminal fragments (β-CTF) is influenced by the GxxxG dimerization motif of the APP transmembrane sequence (TMS) (4,5). β-CTF is the only known γ-secretase substrate comprising a GxxxG motif in triplicate, thus making dimerization of the APP-TMS unique (6).…”

Dimeric structure of transmembrane domain of amyloid precursor protein in micellar environment

“…Familial mutations in the APP TM region presumably affect its structure and lateral mobility in membranes; and alter proteolytic processing with the c-secretase complex. The appearance of data about possibility of APP to dimerize via specific TM helix-helix interactions [5,6] suggests a new insight on the effects of these familial mutations, implying that they could influence the APP self-association in the membrane.…”