Alzheimer-mutant γ-secretase complexes stall amyloid β-peptide production
Missense mutations in the amyloid precursor protein (APP) and presenilin-1 (PSEN1) cause early-onset familial Alzheimer’s disease (FAD) and alter proteolytic production of secreted 38-to-43-residue amyloid β-peptides (Aβ) by the PSEN1-containing γ-secretase complex, ostensibly supporting the amyloid...
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eLife Sciences Publications Ltd
2025-02-01
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| Online Access: | https://elifesciences.org/articles/102274 |
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| author | Parnian Arafi Sujan Devkota Emily Williams Masato Maesako Michael S Wolfe |
| author_facet | Parnian Arafi Sujan Devkota Emily Williams Masato Maesako Michael S Wolfe |
| author_sort | Parnian Arafi |
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| description | Missense mutations in the amyloid precursor protein (APP) and presenilin-1 (PSEN1) cause early-onset familial Alzheimer’s disease (FAD) and alter proteolytic production of secreted 38-to-43-residue amyloid β-peptides (Aβ) by the PSEN1-containing γ-secretase complex, ostensibly supporting the amyloid hypothesis of pathogenesis. However, proteolysis of APP substrate by γ-secretase is processive, involving initial endoproteolysis to produce long Aβ peptides of 48 or 49 residues followed by carboxypeptidase trimming in mostly tripeptide increments. We recently reported evidence that FAD mutations in APP and PSEN1 cause deficiencies in early steps in processive proteolysis of APP substrate C99 and that this results from stalled γ-secretase enzyme-substrate and/or enzyme-intermediate complexes. These stalled complexes triggered synaptic degeneration in a Caenorhabditis elegans model of FAD independently of Aβ production. Here, we conducted full quantitative analysis of all proteolytic events on APP substrate by γ-secretase with six additional PSEN1 FAD mutations and found that all six are deficient in multiple processing steps. However, only one of these (F386S) was deficient in certain trimming steps but not in endoproteolysis. Fluorescence lifetime imaging microscopy in intact cells revealed that all six PSEN1 FAD mutations lead to stalled γ-secretase enzyme-substrate/intermediate complexes. The F386S mutation, however, does so only in Aβ-rich regions of the cells, not in C99-rich regions, consistent with the deficiencies of this mutant enzyme only in trimming of Aβ intermediates. These findings provide further evidence that FAD mutations lead to stalled and stabilized γ-secretase enzyme-substrate and/or enzyme-intermediate complexes and are consistent with the stalled process rather than the products of γ-secretase proteolysis as the pathogenic trigger. |
| format | Article |
| id | doaj-art-916cc4b7e11343349f73ad61d31957a9 |
| institution | Kabale University |
| issn | 2050-084X |
| language | English |
| publishDate | 2025-02-01 |
| publisher | eLife Sciences Publications Ltd |
| record_format | Article |
| series | eLife |
| spelling | doaj-art-916cc4b7e11343349f73ad61d31957a92025-02-11T15:51:10ZengeLife Sciences Publications LtdeLife2050-084X2025-02-011310.7554/eLife.102274Alzheimer-mutant γ-secretase complexes stall amyloid β-peptide productionParnian Arafi0Sujan Devkota1Emily Williams2Masato Maesako3https://orcid.org/0000-0002-1970-2462Michael S Wolfe4https://orcid.org/0000-0002-5721-9092Department of Medicinal Chemistry, University of Kansas, Lawrence, United StatesDepartment of Medicinal Chemistry, University of Kansas, Lawrence, United StatesAlzheimer Research Unit, MassGeneral Institute for Neurodegenerative Disease, Massachusetts General Hospital, Harvard Medical School, Boston, United StatesAlzheimer Research Unit, MassGeneral Institute for Neurodegenerative Disease, Massachusetts General Hospital, Harvard Medical School, Boston, United StatesDepartment of Medicinal Chemistry, University of Kansas, Lawrence, United StatesMissense mutations in the amyloid precursor protein (APP) and presenilin-1 (PSEN1) cause early-onset familial Alzheimer’s disease (FAD) and alter proteolytic production of secreted 38-to-43-residue amyloid β-peptides (Aβ) by the PSEN1-containing γ-secretase complex, ostensibly supporting the amyloid hypothesis of pathogenesis. However, proteolysis of APP substrate by γ-secretase is processive, involving initial endoproteolysis to produce long Aβ peptides of 48 or 49 residues followed by carboxypeptidase trimming in mostly tripeptide increments. We recently reported evidence that FAD mutations in APP and PSEN1 cause deficiencies in early steps in processive proteolysis of APP substrate C99 and that this results from stalled γ-secretase enzyme-substrate and/or enzyme-intermediate complexes. These stalled complexes triggered synaptic degeneration in a Caenorhabditis elegans model of FAD independently of Aβ production. Here, we conducted full quantitative analysis of all proteolytic events on APP substrate by γ-secretase with six additional PSEN1 FAD mutations and found that all six are deficient in multiple processing steps. However, only one of these (F386S) was deficient in certain trimming steps but not in endoproteolysis. Fluorescence lifetime imaging microscopy in intact cells revealed that all six PSEN1 FAD mutations lead to stalled γ-secretase enzyme-substrate/intermediate complexes. The F386S mutation, however, does so only in Aβ-rich regions of the cells, not in C99-rich regions, consistent with the deficiencies of this mutant enzyme only in trimming of Aβ intermediates. These findings provide further evidence that FAD mutations lead to stalled and stabilized γ-secretase enzyme-substrate and/or enzyme-intermediate complexes and are consistent with the stalled process rather than the products of γ-secretase proteolysis as the pathogenic trigger.https://elifesciences.org/articles/102274proteolysissecretasemass spectrometryfluorescence microscopy |
| spellingShingle | Parnian Arafi Sujan Devkota Emily Williams Masato Maesako Michael S Wolfe Alzheimer-mutant γ-secretase complexes stall amyloid β-peptide production eLife proteolysis secretase mass spectrometry fluorescence microscopy |
| title | Alzheimer-mutant γ-secretase complexes stall amyloid β-peptide production |
| title_full | Alzheimer-mutant γ-secretase complexes stall amyloid β-peptide production |
| title_fullStr | Alzheimer-mutant γ-secretase complexes stall amyloid β-peptide production |
| title_full_unstemmed | Alzheimer-mutant γ-secretase complexes stall amyloid β-peptide production |
| title_short | Alzheimer-mutant γ-secretase complexes stall amyloid β-peptide production |
| title_sort | alzheimer mutant γ secretase complexes stall amyloid β peptide production |
| topic | proteolysis secretase mass spectrometry fluorescence microscopy |
| url | https://elifesciences.org/articles/102274 |
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