Impact of Amyloid Precursor Protein Hydrophilic Transmembrane Residues on Amyloid-Beta Generation

Oestereich, Felix; Bittner, Heiko J.; Weise, Christoph; Grohmann, Lisa; Janke, Lisa-Kristin; Hildebrand, Peter W.; Multhaup, Gerhard; Munter, Lisa Marie

doi:10.1021/acs.biochem.5b00217

Cited by 14 publications

(19 citation statements)

References 53 publications

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“…26 Mutating T43 or T48 alters ε-efficiency as well as Aβ42/Aβ40 ratios by shifting ε-site preference. 15,20,21,36 By introducing an additional H-bond, the I45T mutation strengthens the network of H-bonds in TM-C.…”

Section: Discussionmentioning

confidence: 99%

“…Previously, it was shown that Thr residues in the WT C99 TMD (T43 and T48) rigidify the helix by forming H-bonds between their side chains and the main chain 26,35 . Mutations of T43 and T48 to hydrophobic residues (e.g., Val or Ile) affect ε-site preference and efficiency 15,21,36 . Since hydrogen bond networks determine the mechanical and thermodynamic properties of proteins, their alteration in FAD mutants of the APP TMD has been proposed to perturb the fine-tuned interplay of the conformational dynamics of the enzyme and substrate 29 , which is a key factor for substrate recognition and subsequent relaxation steps 37,38 .…”

Section: Introductionmentioning

confidence: 99%

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Increased H-Bond Stability Relates to Altered ε-Cleavage Efficiency and Aβ Levels in the I45T Familial Alzheimer’s Disease Mutant of APP

Götz

Högel

Silber

et al. 2018

Preprint

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1Cleavage of the amyloid precursor protein's (APP) transmembrane domain (TMD) by γ-2 secretase is a crucial step in the etiology of Alzheimer's Disease (AD). Mutations in the APP 3 TMD alter cleavage and lead to familial forms of AD (FAD). The majority of FAD mutations 4 shifts the preference of initial cleavage from ε49 to ε48, thus raising the AD-related Aβ42/Aβ40 5 ratio. The I45T mutation is among the few FAD mutations that do not alter ε-site preference, 6 while it dramatically reduces the efficiency of ε-cleavage. Here we investigate the impact of 7 the I45T mutation on the backbone dynamics of the substrate TMD. Amide exchange 8 experiments and molecular dynamics simulations in solvent and a lipid bilayer reveal an 9 increased stability of amide hydrogen bonds at the ζ-and γ-cleavage sites. Stiffening of the H-10 bond network is caused by an additional H-bond between the T45 side chain and the TMD 11 backbone, which alters dynamics within the cleavage domain. In particular, the increased H-12 bond stability inhibits an upward movement of the ε-sites in the I45T mutant. Thus, an altered 13 presentation of ε-sites to the active site of γ-secretase as a consequence of restricted local 14 flexibility provides a rationale for reduced ε-efficiency of the I45T FAD mutant.15 16 Introduction 1The intramembrane aspartyl protease γ-secretase cleaves the transmembrane domains (TMD) 2 of ~90 bitopic type I transmembrane proteins. 1,2 Due to its involvement in Alzheimer's disease 3 (AD), the amyloid-precursor-protein (APP) is the most extensively studied γ-secretase 4 substrate. 3,4 Prior to cleavage by γ-secretase, APP's ectodomain is shed by β-secretase, thus 5 generating the C99 fragment. Subsequent cleavage of C99 by γ-secretase results in release of 6 the APP intracellular domain (AICD) and β-amyloid (Aβ) peptides of various length. 5 Such 7 step-wise cleavage starts at one of two ε-sites located at the cytosolic border of the C99 TMD 8 between either residue L49 and V50 (ε49) or T48 and L49 (ε48). Cleavage gradually proceeds 9 towards the N-terminus, releasing fragments of three or four residues and leaving Aβ peptides 10 of different length. 6-11 Aβ40, the most abundant Aβ peptide produced from wild-type (WT) 11 C99, is generated by cleavage along the ε49-ζ46-γ43-γ40 pathway. A smaller amount of C99 is 12 processed via cleavage at ε48 and ζ45, leading to Aβ42 and Aβ38 peptides. Of these species, 13Aβ42 is the most aggregation-prone and forms neurotoxic oligomers and plaques. 12,13 The 14 accumulation of plagues consisting of such cell-toxic Aβ peptides in the brain is a central 15 hallmark of AD. 14 In familial forms of AD (FAD) an increased Aβ42/Aβ40 ratio correlates with 16 early onset and fast progression of AD and results from point mutations in C99 or presenilin, 17 the catalytic subunit of γ-secretase. 1,[15][16][17][18][19][20][21] In most mutants, alterations in Aβ42/Aβ40 ratios are 18 linked to shifting the preferential initial cleavage site from ε49 to ε48. However, switching of 19 pathways after ε-cl...

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Increased H-Bond Stability Relates to Altered ε-Cleavage Efficiency and Aβ Levels in the I45T Familial Alzheimer’s Disease Mutant of APP

Götz

Högel

Silber

et al. 2018

Preprint

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“…For instance, the substitution of a single leucine by glycine in a membrane spanning poly-L helix facilitates helix bending, enhances local hydration, and triggers a redistribution of α-helical and 3 10 helical H-bonds (34). The view that global TMD flexibility is required for efficient cleavage of C99 is further supported by biochemical analyses, which showed that mutations introduced at sites that are even farther from the cleavage region, can shift cleavage sites as well as cleavage efficiency (35)(36)(37). Furthermore, a detailed recent analysis showed that helix-instability of the C99 TMD caused by the introduction of helix-destabilizing di-glycine motifs in the domain near the ε-sites enhance the initial cleavage and subsequent carboxy-terminal trimming (38).…”

Section: Instroductionmentioning

confidence: 96%

Modulating hinge flexibility in the APP transmembrane domain alters γ-secretase cleavage

Götz¹,

Mylonas²,

Högel³

et al. 2018

Preprint

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Intramembrane cleavage of the β-amyloid precursor protein C99 substrate by γsecretase is implicated in Alzheimer´s disease pathogenesis. Since conformational flexibility of a di-glycine hinge in the C99 transmembrane domain (TMD) might be critical for γ-secretase cleavage, we mutated one of the glycine residues, G38, to a helixstabilizing leucine and to a helix-distorting proline. CD, NMR and hydrogen/deuterium exchange measurements as well as MD simulations showed that the mutations distinctly altered the intrinsic structural and dynamical properties of the TMD. However, although helix destabilization/unfolding was not observed at the initial ε-cleavage sites of C99, both mutants impaired γ-secretase cleavage and altered its cleavage specificity. Moreover, helix flexibility enabled by the di-glycine hinge translated to motions of other helix parts. Our data suggest that both local helix stabilization and destabilization in the di-glycine hinge may decrease the occurrence of enzyme-substrate complex conformations required for normal catalysis and that hinge mobility can be conducive for productive substrate-enzyme interactions.

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“…Overall, it is clear that ⑀-cleavage is a limiting step for the subsequent ␥-secretase ␥-cuts. Oestereich et al (51) have shown that AICD 50 -99 (VMLKKK . .…”

Section: Possible Sources Of Nuclear Aicd A␤ and Taumentioning

confidence: 99%

“…The major processing routes converge at A␤34, which is further hydrolyzed into A␤30 (50). The N-terminal half of the TMS of APP is stabilized the GXXXG interaction motif with Gly-29 and Gly-33 (in red) as the central residues (51,96,97). In addition to familial mutations (98), e.g.…”

Section: Aicd A␤42 and Tau Interactions With Dnamentioning

confidence: 99%

Amyloid Precursor Protein (APP) Metabolites APP Intracellular Fragment (AICD), Aβ42, and Tau in Nuclear Roles

Multhaup

Huber

Buée

et al. 2015

Journal of Biological Chemistry

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Alzheimer disease (AD) 2 is the most common form of dementia and a leading cause of death. Amyloid-␤ (A␤) peptides of varying length (30 -51 amino acid residues) are produced by the sequential, proteolytic processing of the amyloid precursor protein (APP) by ␤-and ␥-secretases (1, 2). In the healthy brain, these protein fragments are normally degraded and eliminated. In the AD brain, the 42-amino acid peptide (A␤42) is prone to form aggregated amyloid oligomers, which are believed to contribute to plaque formation and cognitive decline (3-6).The ␥-secretase also liberates an intracellular fragment called AICD composed of up to 50 residues depending on N-terminal variations (7-9). The first identification of the APP intracellular fragment (AICD) and its detection in brain tissue (8) immediately suggested that it has transcriptional activity, like the Notch intracellular domain (NICD). Whether amyloid A␤ represents a biologically inert bypass product of APP processing or can harbor its own function is a leading question in the AD field. A␤ is potentially toxic depending on its biophysical state (10). Equimolar amounts of the A␤ peptides and the C-terminal fragment AICD are derived from the ␤-C-terminal fragment C99 (11), which represents the APP fragment generated by the initial APP cleavage by ␤-secretase (Fig. 1).A seminal discovery concerning the transcriptional regulatory function of the APP cytoplasmic tail was the observation of its complex formation with Fe65 and the histone acetyltransferase Tip60 and transcriptional activity in reporter gene assays (12). Transactivation of transcription requires ␥-secretase activity and nuclear translocation of Fe65 but not of AICD under these assay conditions (13). However, other studies detected AICD in transcriptional complexes on promoters of target genes using ChIP (see below).In addition, there is evidence that soluble APP fragments (sAPP) of the ectodomain can modulate gene transcription in stimulating downstream signaling through unknown sAPP receptor(s) (14). Accumulation of intracellular A␤ species in neuronal cells before plaque formation leading to concomitant loss of MAP2 expression suggested that A␤ may affect expression or turnover of other proteins (15-17). However, it was not clarified whether this occurs at the transcriptional or translational level.Using a variety of techniques, the recently detected uptake of A␤ peptides into the nuclei of cultured cells (as well as in vivo) revealed that A␤42 possesses unique modulatory activity (18). Direct evidence for the presence of (i) nuclear A␤42 in wildtype animals, (ii) the increased level of nuclear A␤42 in APPoverexpressing animals, and (iii) the detection of nuclear A␤ in quantities comparable with other transcription factors imply a certain biological relevance.The second major hallmark of AD pathology is the presence of neurofibrillary tangles and is associated with intracellular Tau aggregates called neurofibrillary tangles and with modified Tau (19). Although the neuronal Tau (tubulin-associated unit...

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Impact of Amyloid Precursor Protein Hydrophilic Transmembrane Residues on Amyloid-Beta Generation

Cited by 14 publications

References 53 publications

Increased H-Bond Stability Relates to Altered ε-Cleavage Efficiency and Aβ Levels in the I45T Familial Alzheimer’s Disease Mutant of APP

Increased H-Bond Stability Relates to Altered ε-Cleavage Efficiency and Aβ Levels in the I45T Familial Alzheimer’s Disease Mutant of APP

Modulating hinge flexibility in the APP transmembrane domain alters γ-secretase cleavage

Amyloid Precursor Protein (APP) Metabolites APP Intracellular Fragment (AICD), Aβ42, and Tau in Nuclear Roles

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