Alanine substitutions in the GXXXG motif alter C99 cleavage by γ‐secretase but not its dimerization

The amyloid β (Aβ) protein is a major component of senile plaques, one of the neuropathological hallmarks of Alzheimer's disease. Amyloidogenic processing of amyloid precursor protein (APP) by β‐ and γ‐secretases leads to production of Aβ. APP contains tandem triple repeats of the GXXXG motif i...

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Veröffentlicht in:Journal of neurochemistry 2017-03, Vol.140 (6), p.955-962
Hauptverfasser: Higashide, Hidekazu, Ishihara, Seiko, Nobuhara, Mika, Ihara, Yasuo, Funamoto, Satoru
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Sprache:eng
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Zusammenfassung:The amyloid β (Aβ) protein is a major component of senile plaques, one of the neuropathological hallmarks of Alzheimer's disease. Amyloidogenic processing of amyloid precursor protein (APP) by β‐ and γ‐secretases leads to production of Aβ. APP contains tandem triple repeats of the GXXXG motif in its extracellular juxtamembrane and transmembrane regions. It is reported that the GXXXG motif is related to protein–protein interactions, but it remains controversial whether the GXXXG motif in APP is involved in substrate dimerization and whether dimerization affects γ‐secretase‐dependent cleavage. Therefore, the relationship between the GXXXG motifs, substrate dimerization, and γ‐secretase‐dependent cleavage sites remains unclear. Here, we applied blue native poly acrylamide gel electrophoresis to examine the effect of alanine substitutions within the GXXXG motifs of APP carboxyl terminal fragment (C99) on its dimerization and Aβ production. Surprisingly, alanine substitutions in the motif failed to alter C99 dimerization in detergent soluble state. Cell‐based and solubilized γ‐secretase assays demonstrated that increasing alanine substitutions in the motif tended to decrease long Aβ species such as Aβ42 and Aβ43 and to increase in short Aβ species concomitantly. Our data suggest that the GXXXG motif is crucial for Aβ production, but not for C99 dimerization. Amyloidogenic processing of amyloid precursor protein (APP) leads to production of Aβ by β‐ and γ‐secretases. APP contains tandem triple repeats of the GXXXG motif in its extracellular juxtamembrane and transmembrane regions. Here, we demonstrated that alanine substitutions in the GXXXG motif failed to alter dimerization of carboxyl terminal fragment of APP (C99), a direct substrate of γ‐secretase and tended to exhibit a decrease in Aβ42 production and a concomitant increase in Aβ38 production. Our data suggest that GXXXG motif is crucial for Aβ production, but not for C99 dimerization.
ISSN:0022-3042
1471-4159
DOI:10.1111/jnc.13942