APH1 Polar Transmembrane Residues Regulate the Assembly and Activity of Presenilin Complexes

Abstract

Complexes involved in the γ/ϵ-secretase-regulated intramembranous proteolysis of substrates such as the amyloid-β precursor protein are composed primarily of presenilin (PS1 or PS2), nicastrin, anterior pharynx defective-1 (APH1), and PEN2. The presenilin aspartyl residues form the catalytic site, and similar potentially functional polar transmembrane residues in APH1 have been identified. Substitution of charged (E84A, R87A) or polar (Q83A) residues in TM3 had no effect on complex assembly or activity. In contrast, changes to either of two highly conserved histidines (H171A, H197A) located in TM5 and TM6 negatively affected PS1 cleavage and altered binding to other secretase components, resulting in decreased amyloid generating activity. Charge replacement with His-to-Lys substitutions rescued nicastrin maturation and PS1 endoproteolysis leading to assembly of the formation of structurally normal but proteolytically inactive γ-secretase complexes. Substitution with a negatively charged side chain (His-to-Asp) or altering the structural location of the histidines also disrupted γ-secretase binding and abolished functionality of APH1. These results suggest that the conserved transmembrane histidine residues contribute to APH1 function and can affect presenilin catalytic activity.

Proliferation, differentiation and amyloid-β production in neural progenitor cells isolated from TgCRND8 mice

“…The ELISA (Biosource International) was performed as previously described (Pardossi-Piquard et al, 2009). For Aβ quantification, neurosphere media was conditioned for 4 days with samples taken from paired cultures (Non-Tg and TgCRND8) between passages 3 and 7.…”

The very many faces of presenilins and the γ-secretase complex

“…Loss of any subunit abolishes proteolysis (Pardossi-Piquard et al 2009). However, some experimental lines of evidence clearly suggest that in some cases not all subunits are required for proteolytic activity of the complex.…”

Presenilins and -Secretase: Structure, Function, and Role in Alzheimer Disease

“…Which components are bound to each other, and what are the binding domains? Nicastrin and Aph-1 form an initial subcomplex in the endoplasmic reticulum , and multiple TMDs of Aph-1 are involved in the binding to Nicastrin (Pardossi-Piquard et al 2009;Chiang et al 2010). The Nicastrin/ Aph-1 subcomplex then interacts with the PSEN and Pen-2 subcomplex (Fraering et al 2004a).…”