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Fibril branching dominates self-assembly of mutant huntingtin exon-1 aggregates in vitro

Item Type:Preprint
Title:Fibril branching dominates self-assembly of mutant huntingtin exon-1 aggregates in vitro
Creators Name:Wagner, A.S. and Politi, A.Z. and Steinhof, A. and Bravo-Rodriguez, K. and Buntru, A. and Strempel, N.U. and Brusendorf, L. and Haenig, C. and Boeddrich, A. and Plassmann, S. and Ramirez-Anguita, J.M. and Baum, K. and Sanchez-Garcia, E. and Wolf, J. and Wanker, E.E.
Abstract:Huntingtin (HTT) fragments with extended polyglutamine (polyQ) tracts self-assemble into amyloid-like fibrillar aggregates. Elucidating the fibril formation mechanism is critical for understanding Huntington's disease pathology and for developing novel therapeutic strategies. Here, we performed systematic experimental and theoretical studies to examine the self-assembly of an aggregation-prone N-terminal HTT exon-1 fragment with 49 glutamines (Ex1Q49). We demonstrate that two nucleation mechanisms control spontaneous Ex1Q49 fibrillogenesis: (1) a relatively slow primary fibril-independent nucleation process, which involves the spontaneous formation of aggregation-competent monomers, and (2) a fast secondary fibril-dependent nucleation process, which involves branching and promotes the rapid assembly of highly complex fibril bundles with multiple ends. The proposed aggregation mechanism is supported by studies with the small molecule O4, which perturbs primary nucleation and delays Ex1Q49 fibril assembly, comprehensive mathematical and computational modelling studies, and seeding experiments with small, preformed fibrillar Ex1Q49 aggregates. All results indicate that in vitro, HTT exon-1 fibrillar aggregates are formed by a branching mechanism.
Keywords:Huntingtin Fibrillogenesis, Aggregation Mechanism,, Primary and Secondary Nucleation, Amyloidogenesis, Fibril Branching
Source:bioRxiv
Publisher:Cold Spring Harbor Laboratory (U.S.A.)
Article Number:195297
Date:19 October 2017
Official Publication:https://doi.org/10.1101/195297

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