Ubiquitination Can Change the Structure of the α-Synuclein Amyloid Fiber in a Site Selective Fashion

Abstract

Toxic amyloid aggregates are a feature of many neurodegenerative diseases. A number of biochemical and structural studies have demonstrated that not all amyloids of a given protein are equivalent but rather that an aggregating protein can form different amyloid structures or polymorphisms. Different polymorphisms can also induce different amounts of pathology and toxicity in cells and in mice, suggesting that the structural differences may play important roles in disease. However, the features that cause the formation of polymorphisms in vivo are still being uncovered. Posttranslational modifications on several amyloid forming proteins, including the Parkinson’s disease causing protein α-synuclein, may be one such cause. Here, we explore whether ubiquitination can induce structural changes in α-synuclein aggregates in vitro. We used protein chemistry to first synthesize ubiquitinated analogues at three different positions using disulfide linkages. After aggregation, these linkages can be reversed, allowing us to make relative comparisons between the structures using a proteinase K assay. We find that, while ubiquitination at residue 6, 23, or 96 inhibits α-synuclein aggregation, only modification at residue 96 causes an alteration in the aggregate structure, providing further evidence that posttranslational modifications may be an important feature in amyloid polymorphism formation.

Modulation of the Interactions Between α-Synuclein and Lipid Membranes by Post-translational Modifications

“…This approach showed that K6-ubiquitin and K23-ubiquitin both inhibit fibril formation, but do not alter the structure of fibrils. However, K96-ubiquitin inhibits aggregation and also alters structure of aggregates formed (157).…”

Alpha-synuclein research: defining strategic moves in the battle against Parkinson’s disease

“…Although recent studies have shown that ubiquitination and nitration of monomeric aSyn change dramatically the morphology and structure of the fibrils 128 in a site-specific manner, there are no reports in the literature on how PTMs influence the structural and toxic properties of aSyn oligomers. Therefore, further studies are needed to determine at what stages during aSyn aggregation and LB formation are different PTMs introduced and how they influence these processes and aSyn-induced toxicity.…”

Atypical Ubiquitination and Parkinson’s Disease

“…Alpha-synuclein has been shown to be monoubiquitinated by the E3 ubiquitin ligase SIAH (seven in absentia homolog) both in vivo and in vitro [ 43 , 44 , 45 ]. The ubiquitination at certain lysine residues induces structural changes in alpha-synuclein aggregates in vitro [ 46 ]. Synphilin-1A, an isoform of synphilin-1 (another component of Lewy bodies), inhibits alpha-synuclein monoubiquitination by SIAH and the formation of alpha-synuclein inclusions [ 47 ].…”