Journal Article

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

Mann, Matthias, Pinkert, Stefan, Hornburg, Daniel, Hastie, Alex R., Hartl, F. Ulrich, Kömer, Roman, Hipp, Mark S., Chumakova, Victoria, Antonin, Matthias, Ruff, Kiersten M., Pappu, Rohit V., Ripaud, Leslie

2014

Overview

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. Significance Expansion of a poly-glutamine (polyQ) repeat is the causal mutation of several inherited neurological disorders, including Huntington’s disease. In a yeast genetic screen, we identified several proteins with Q-rich, prion-like domains that reduce the toxicity of mutant polyQ proteins when overexpressed. One of these, glycine threonine serine repeat protein (Gts1p), was characterized in more detail. Association with Gts1p did not prevent aggregation but altered the physical properties and the interactome of the aggregates. Specifically, Gts1p expression reduced the sequestration of other prion-like proteins into the polyQ aggregates. These findings link polyQ toxicity in yeast with the coaggregation of prion proteins and show that short Q-rich peptides are able to shield toxic forms of polyQ proteins, directing them into nontoxic aggregates.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Aggregates / Aggregation / Binding sites / Biological Sciences / Cell aggregates / Cytotoxicity / gene overexpression / Genetic screening / Huntington disease / Molecular interactions / Molecules / mutants / mutation / nervous system diseases / Neurochemistry / Neurodegeneration / Neurodegenerative diseases / Peptides / Peptides - metabolism / Physical properties / Prions / Prions - metabolism / Protein Binding / Protein expression / Proteins / Saccharomyces cerevisiae / Saccharomyces cerevisiae - genetics / serine / threonine / Yeast / Yeasts