Abstract
Aggregation of amyloidogenic proteins is an abnormal biological process implicated in neurodegenerative disorders. Whereas the aggregation process of amyloid-forming proteins has been studied extensively, the mechanism of aggregate removal is poorly understood. We recently demonstrated that proteasomes could fragment filamentous aggregates into smaller entities, restricting aggregate size [1]. Here, we show in vitro that UBE2W can modify the N-terminus of both α-synuclein and a tau tetra-repeat domain with a single ubiquitin. We demonstrate that an engineered N-terminal ubiquitin modification changes the aggregation process of both proteins, resulting in the formation of structurally distinct aggregates. Single-molecule approaches further reveal that the proteasome can target soluble oligomers assembled from ubiquitin-modified proteins independently of its peptidase activity, consistent with our recently reported fibril-fragmenting activity. Based on these results, we propose that proteasomes are able to target oligomers assembled from N-terminally ubiquitinated proteins. Our data suggest a possible disassembly mechanism by which N-terminal ubiquitination and the proteasome may together impede aggregate formation.
Highlights
The 26S proteasome holoenzyme is responsible for selective protein degradation in eukaryotic cells [2]
The proteolytic activity required for degradation is provided by the 20S core particle (CP) of the holoenzyme, whereas the 19S regulatory particle (RP) that caps the CP on one or both ends is responsible for substrate recognition and ATP-dependent substrate unfolding and translocation into the CP [3e5]
Aggregates assembled from amyloidogenic proteins tau and a-synuclein have been implicated in Alzheimer disease (AD) and Parkinson disease (PD), respectively [9,10]
Summary
The 26S proteasome holoenzyme is responsible for selective protein degradation in eukaryotic cells [2]. Many biological processes are dependent on the proteasome through controlled degradation of key regulatory factors, including homeostasis, unfolded protein response, and proteostasis [6]. Aggregates assembled from amyloidogenic proteins tau and a-synuclein (aS) have been implicated in Alzheimer disease (AD) and Parkinson disease (PD), respectively [9,10]. Both tau and aS are intrinsically disordered in their nonamyloid state as monomers and have been reported to be degradation-resistant as aggregates [11e14]
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