The relationship between aggregation and toxicity of polyglutamine-containing ataxin-3 in the intracellular environment of Escherichia coli.

Abstract

Several neurodegenerative diseases are triggered by proteins containing a polyglutamine (polyQ) stretch expanded beyond a critical threshold. Among these, ataxin-3 (AT3) is the causative agent of spinocerebellar ataxia type-3. We expressed three authentic AT3 variants in Escherichia coli: one normal (AT3-Q24), one expanded (AT3-Q55) and one truncated immediately upstream of the polyQ (AT3-291Δ). Then, based on growth rate reduction, we quantified protein toxicity. We show that AT3-Q55 and -291Δ strongly reduced the growth rate in the early stages (2-4 h), unlike AT3-Q24. This correlated well with the appearance of soluble cytosolic oligomers, but not with the amount of insoluble protein in inclusion bodies (IBs). The impact of AT3-291Δ on cell growth suggests an intrinsic toxicity of the AT3 fragment. Besides the typical Fourier Transform Infrared Spectroscopy (FTIR) signal for intermolecular β-sheets, the expanded form displayed an additional infrared signature, which was assigned to glutamine side-chain hydrogen bonding and associated with SDS-insoluble fibrils. The elongation of the latter was monitored by Atomic Force Microscopy (AFM). This mirrors the well-known in vitro two-step aggregation pattern of expanded AT3. We also demonstrated that final aggregates of strains expressing expanded or truncated AT3 play a protective role against toxicity. Furthermore, our findings suggest that the mechanisms of toxicity are evolutionarily conserved.

• Authors: Gaetano Invernizzi, Francesco A Aprile, Antonino Natalello, Andrea Ghisleni, Amanda Penco, Annalisa Relini, Silvia M Doglia, Paolo Tortora, Maria E Regonesi
• Journal: PloS one (PLoS One) Vol. 7 Issue 12 Pg. e51890 ( 2012) ISSN: 1932-6203 [Electronic] United States
• PMID: 23251648 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Nerve Tissue Proteins
• Nuclear Proteins
• Peptides
• polyglutamine

Topics

• Escherichia coli (genetics, metabolism)
• Hydrogen Bonding
• Inclusion Bodies (chemistry, metabolism)
• Nerve Tissue Proteins (chemistry, genetics, metabolism)
• Nuclear Proteins (chemistry, genetics, metabolism)
• Peptides (chemistry, metabolism)
• Protein Structure, Secondary