Two domains within the first putative transmembrane domain of presenilin 1 differentially influence presenilinase and γ‐secretase activity

Abstract

Presenilins (PS) are thought to contain the active site for presenilinase endoproteolysis of PS and c-secretase cleavage of substrates. The structural requirements for PS incorporation into the c-secretase enzyme complex, complex stability and maturation, and appropriate presenilinase and c-secretase activity are poorly understood. We used rescue assays to identify sequences in transmembrane domain one (TM1) of PS1 required to support presenilinase and c-secretase activities. Swap mutations identified an N-terminal TM1 domain that is important for c-secretase activity only and a C-terminal TM1 domain that is essential for both presenilinase and c-secretase activities. Exchange of residues 95-98 of PS1 (sw95-98) completely abolishes both activities while the familial Alzheimer's disease mutation V96F significantly inhibits both activities. Reversion of residue 96 back to valine in the sw95-98 mutant rescues PS function, identifying V96 as the critical residue in this region. The TM1 mutants do not bind to an aspartyl protease transition state analog c-secretase inhibitor, indicating a conformational change induced by the mutations that abrogates catalytic activity. TM1 mutant PS1 molecules retain the ability to interact with c-secretase substrates and c-secretase complex members, although Nicastrin stability is decreased by the presence of these mutants. c-Secretase complexes that contain V96F mutant PS1 molecules display a partial loss of function for c-secretase that alters the ratio of amyloid-b peptide species produced, leading to the amyloid-b peptide aggregation that causes familial Alzheimer's disease.

A C-terminal Region of Signal Peptide Peptidase Defines a Functional Domain for Intramembrane Aspartic Protease Catalysis

“…However, the N terminus appears to serve an essential role in supporting this functional domain and is postulated to be a structural scaffold (2). Also, biochemical studies of presenilin indicate the N terminus is crucial for activity (24). Nevertheless, our findings indicate that a conserved C-terminal region of SPP is sufficient for the proteolytic activity and suggests a novel structural feature of SPP compared with other I-CLiPs.…”

Participation of Transmembrane Domain 1 of Presenilin 1 in the Catalytic Pore Structure of the γ-Secretase

“…Notably, the Cys substitution of V96, located at the opposite side of V94 in an ␣-helical model, caused a loss of protein expression. Consistently, TMD1 is involved in the stabilization of the ␥-secretase after the complex assembly is completed (Brunkan et al, 2005;Watanabe et al, 2010). Moreover, amino acid alignment also revealed that V96 is highly conserved from plants to mammals (supplemental Fig.…”

“…Transmembrane helix kinks commonly occur at proline residues (von Heijne, 1991). It has also been suggested that mutations of the N-and C-terminal regions of TMD1 differentially affected the PS endoproteolysis and the ␥-secretase activity (Brunkan et al, 2005). Consistently, we showed that N-and C-terminal portions of TMD1 divided by the PV motif exhibit distinct labeling patters by MTS reagent: consecutive residues from G78 to L85 were accessible to MTSEAbiotin, whereas V94C was the only labeled residue in the C-terminal region of TMD1.…”

Assembly, Maturation, and Trafficking of the γ-Secretase Complex in Alzheimers Disease

“…(3)). A third functional determinant was recently identified in the TMD1 of PS: the N-terminal portion of TMD1 affects only -secretase activity, while only the Cterminal portion of TMD1 is responsible for PS endoproteolysis [83]. Finally, a second APP-binding site separate from, but near to, the -secretase active site was recently identified [84][85][86][87][88][89].…”