P004 - THE GENETIC LANDSCAPE FOR AMYLOID BETA NUCLEATION ACCURATELY DISCRIMINATES FAMILIAL ALZHEIMER’S DISEASE MUTATIONS
Abstract
Aims
Amyloid plaques of the amyloid beta (Aß) peptide are a universal pathological hallmark of Alzheimer's disease (AD) and mutations in Aß cause familial forms of AD (fAD) . However, the molecular mechanism by which these mutations cause fAD remains unclear and the vast majority of mutations in Aß are variants of uncertain clinical significance. Here, we set out to identify all of the mutations in Aß that are likely to cause these rare forms of AD, by measuring their ability to nucleate amyloids in vivo.
Methods
To do so, we have recently developed a deep mutagenesis method that quantifies the ability of thousands of protein variants to nucleate the formation of amyloid fibrils in vivo. By this means, we could quantify amyloid nucleation for more than 14,000 variants of Aß.
Results
As a result, we provide the first description of how mutations alter the nucleation of any amyloid fibril. Our results reveal a modular organisation of mutational effects along the Aß sequence and uncover the role of charge and specific gatekeeper residues in the disordered N-terminus in preventing the nucleation of amyloids. Strikingly, the in vivo nucleation scores, unlike computational predictors and previous measurements, accurately discriminate all the known dominant fAD mutations. This suggests that accelerated nucleation is the fundamental molecular mechanism by which mutations cause fAD.
Conclusions
Taken together, these results provide the first global picture of how sequence changes prevent and promote the nucleation of amyloid fibrils and provide a clinically-validated resource for the future interpretation of genetic variation in Aß.
