Structural Basis Of γ-secretase Inhibition And Modulation By Small Molecule Drugs

Alzheimer’s disease(AD)is the most common dementia worldwide.A hallmark of Alzheimer’s disease is accumulation of β-amyloid plaque in the brains of patients.Amyloid precursor protein(APP)is proteolyzed by β-secretase and γ-secretase to generate β-amyloid peptide(Aβ)of varying lengths,the main component of β-amyloid plaque.Mature γ-secretase consists of four subunits: Presenilin(PS),Nicastrin(NCT),Aph-1 and Pen-2.Presenilin,the component responsible for the proteolytic activity,contains two orthologues,PS1 and PS2,which have different cellular location and cleavage activity.Many familial AD(FAD)related mutations are identified on APP and PS,which elevate the ratio of Aβ42 to Aβ40.Development of γ-secretase inhibitors(GSIs)and modulators(GSMs)to its cleavage activity represents an attractive therapeutic opportunity for AD and cancers.However,how these GSIs and GSMs target γ-secretase has remained largely unclear.To clarify the recognition of GSIs by γ-secretase,we determined the cryo-electron microscopy(cryo-EM)structures of human γ-secretase bound individually to a transition state analog(TSA)GSI L685,458,an AD clinical candidate Semagacestat,and five clinical candidates for cancer at atomic resolution.Remarkably,each of the GSIs occupies the same general location on PS1 that accommodates the β-strand from APP or Notch,interfering with substrate recruitment.L685,458 directly coordinates the two catalytic aspartate residues of PS1.Structural analysis and comparison reveal a shared theme for GSI recognition,which will guide development of more efficient inhibitors.About 150 proteins have been identified as γ-secretase substrates to date.Selective inhibitors maybe relieve toxicity in the clinical evaluation of GSIs.We determined the cryo-electron microscopy(cryo-EM)structures of human γ-secretase bound with an APPselective inhibitor Avagacestat,a PS1-selective inhibitor MRK-560,and a classic γ-secretase modulator E2012.The APP β-strand region may be responsible for selective inhibition of Avagacestat.Thr281 and Leu282 in loop-2 of PS1 are the determinant for isoform-dependent sensitivity to MRK-560.And E2012 binds to an allosteric site of γ-secretase on the extracellular side,potentially explaining its modulating activity.Our analysis reveals an important framework for future development of selective GSIs and next generation GSMs.