Overexpression of Q-rich prion-like proteins suppresses polyQ cytotoxicity and alters the polyQ interactome

Abstract

Expansion of a poly-glutamine (polyQ) repeat in a group of functionally unrelated proteins is the cause of several inherited neurodegenerative disorders, including Huntington's disease. The polyQ length-dependent aggregation and toxicity of these disease proteins can be reproduced in Saccharomyces cerevisiae. This system allowed us to screen for genes that when overexpressed reduce the toxic effects of an N-terminal fragment of mutant huntingtin with 103 Q. Surprisingly, among the identified suppressors were three proteins with Q-rich, prion-like domains (PrDs): glycine threonine serine repeat protein (Gts1p), nuclear polyadenylated RNA-binding protein 3, and minichromosome maintenance protein 1. Overexpression of the PrD of Gts1p, containing an imperfect 28 residue glutamine-alanine repeat, was sufficient for suppression of toxicity. Association with this discontinuous polyQ domain did not prevent 103Q aggregation, but altered the physical properties of the aggregates, most likely early in the assembly pathway, as reflected in their increased SDS solubility. Molecular simulations suggested that Gts1p arrests the aggregation of polyQ molecules at the level of nonfibrillar species, acting as a cap that destabilizes intermediates on path to form large fibrils. Quantitative proteomic analysis of polyQ interactors showed that expression of Gts1p reduced the interaction between polyQ and other prion-like proteins, and enhanced the association of molecular chaperones with the aggregates. These findings demonstrate that short, Q-rich peptides are able to shield the interactive surfaces of toxic forms of polyQ proteins and direct them into nontoxic aggregates.protein aggregation | protein misfolding | neurodegeneration | prion | polyglutamine proteins

The Social Amoeba Dictyostelium discoideum Is Highly Resistant to Polyglutamine Aggregation

“…Like seeds, Dictyostelium spores are desiccation-resistant, raising a potential role for hydrophilic amino acid repeats protecting against protein aggregation in spores. Consistent with this, glutamine-rich prion-like proteins have been shown to prevent polyglutamine toxicity in yeast (34,35). Further work to identify the endogenous role of proteins containing amino acid repeats in Dictyostelium is warranted and may provide insight into unique properties of these proteins.…”

Profilin reduces aggregation and phase separation of huntingtin N-terminal fragments by preferentially binding to soluble monomers and oligomers

“…In the polyQ:Pfn interaction model, the auxiliary interaction is between the polyQ bead of a Q 40 -C38 molecule and a nonspecific region on the profilin molecule that is distinct from the polyP binding site (Figure 6b). This model accounts for experimental results, which suggest that long polyQ tracts and polyQ aggregates can interact non-specifically with other molecules given the uniformly "sticky" surface of the polyQ domain (73)(74)(75)(76). This model allows for the possibility of a heterotypic multivalent complex in which a single profilin molecule is engaged in two different types of interactions with a Q 40 -C38 oligomer.…”

“…Htt-NTFs engage in a wide variety of proteinprotein interactions (75,(81)(82)(83)(84)(85)(86)(87)(88)(89)(90). These "interactomes" are tissue-specific and within a tissue-type, the nodes and edges in an interaction network are known to be different for Htt-NTFs with wild-type versus mutant polyQ lengths (90).…”

Prions: What Are They Good For?

“…Alternatively, pathogenic amyloids may directly interact with functional amyloids, either by sequestering or perturbing their counterparts (Figure 8). Cross-seeding, although rare and inefficient, occurs among different amyloids and aggregate-prone proteins (Derkatch et al 2004, Giasson et al 2003, Kotzbauer et al 2004, Ripaud et al 2014. Therefore, although a slow event, the accumulation of toxic amyloids over time may guide functional amyloids to attain a nonfunctional or toxic state and lose functional capacity.…”