Center of Functional Protein Assemblies, Technical University of Munich, Garching, Germany.
German Center for Neurodegenerative Diseases (DZNE), Munich, Germany.
Commun Biol. 2023 Jun 24;6(1):670. doi: 10.1038/s42003-023-05039-y.
γ-Secretase is an aspartyl intramembrane protease that cleaves the amyloid precursor protein (APP) involved in Alzheimer's disease pathology and other transmembrane proteins. Substrate-bound structures reveal a stable hybrid β-sheet immediately following the substrate scissile bond consisting of β1 and β2 from the enzyme and β3 from the substrate. Molecular dynamics simulations and enhanced sampling simulations demonstrate that the hybrid β-sheet stability is strongly correlated with the formation of a stable cleavage-compatible active geometry and it also controls water access to the active site. The hybrid β-sheet is only stable for substrates with 3 or more C-terminal residues beyond the scissile bond. The simulation model allowed us to predict the effect of Pro and Phe mutations that weaken the formation of the hybrid β-sheet which were confirmed by experimental testing. Our study provides a direct explanation why γ-secretase preferentially cleaves APP in steps of 3 residues and how the hybrid β-sheet facilitates γ-secretase proteolysis.
γ-分泌酶是一种天冬氨酸跨膜蛋白酶，可切割淀粉样前体蛋白（APP），该蛋白参与阿尔茨海默病的病理过程及其他跨膜蛋白。底物结合结构揭示了在底物切口键之后紧接着存在稳定的混合β-片层，其由酶的β1 和β2 以及底物的β3 组成。分子动力学模拟和增强采样模拟表明，混合β-片层的稳定性与形成稳定的可切割活性构象密切相关，它还控制着水进入活性位点。混合β-片层仅对在切口键后具有 3 个或更多 C 末端残基的底物稳定。该模拟模型使我们能够预测削弱混合β-片层形成的 Pro 和 Phe 突变的影响，实验测试证实了这一点。我们的研究提供了一个直接的解释，说明为什么 γ-分泌酶优先以 3 个残基的步长切割 APP，以及混合β-片层如何促进 γ-分泌酶蛋白水解。
