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Critical nucleus size for disease-related polyglutamine aggregation is repeat-length dependent

Nature Structural & Molecular Biology volume 18, pages 328–336 (2011)Cite this article

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Abstract

Because polyglutamine (polyQ) aggregate formation has been implicated as playing an important role in expanded CAG repeat diseases, it is important to understand the biophysics underlying the initiation of aggregation. Previously, we showed that relatively long polyQ peptides aggregate by nucleated growth polymerization and a monomeric critical nucleus. We show here that over a short range of repeat lengths, from Q23 to Q26, the size of the critical nucleus for aggregation increases from monomeric to dimeric to tetrameric. This variation in nucleus size suggests a common duplex antiparallel β-sheet framework for the nucleus, and it further supports the feasibility of an organized monomeric aggregation nucleus for longer polyQ repeat peptides. The data also suggest that a change in the size of aggregation nuclei may have a role in the pathogenicity of polyQ expansion in this series of familial neurodegenerative diseases.

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Figure 1: Effect of AT7NT on polyQ aggregation kinetics.
Figure 2: Transmission electron micrograph images obtained for different peptides incubated in PBS buffer at 37°C.
Figure 3: Aggregation kinetics analysis of the peptide SFQ37P10K2.
Figure 4: Aggregation kinetics of peptide K2Q37K2 in PBS at 37°C.
Figure 5: DLS analysis of the aggregation reaction of K2Q23K2 at 215 μM.
Figure 6: Kinetic analysis of K2Q23K2 by sedimentation assay.
Figure 7: Log-log plots of initial reaction rates versus initial concentration.
Figure 8: Further nucleation kinetics analysis of K2Q23K2.
Figure 9: Models of nucleated growth polymerization.

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Acknowledgements

We acknowledge access to the PONDR® analysis, provided by Molecular Kinetics. We thank G. Calero for access to his dynamic light-scattering instrument. EMs were collected in the University of Pittsburgh School of Medicine Structural Biology Department's EM facility administered by J. Conway and A. Makhov. We gratefully acknowledge funding support from US National Institutes of Health grants R01 AG019322 and R21 AG033757 (R.W.).

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Authors and Affiliations

  1. Structural Biology Department, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA

    Karunakar Kar, Murali Jayaraman, Bankanidhi Sahoo, Ravindra Kodali & Ronald Wetzel

  2. Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA

    Karunakar Kar, Murali Jayaraman, Bankanidhi Sahoo, Ravindra Kodali & Ronald Wetzel

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Contributions

K.K., M.J. and B.S. purified the peptides, determined and analyzed the aggregation kinetics and obtained dynamic light-scattering data on aggregation time points. R.K. obtained the EM and FTIR data. R.W. wrote the paper. All authors contributed to study design, data interpretation and improving the manuscript.

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Correspondence to Ronald Wetzel.

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Kar, K., Jayaraman, M., Sahoo, B. et al. Critical nucleus size for disease-related polyglutamine aggregation is repeat-length dependent. Nat Struct Mol Biol 18, 328–336 (2011). https://doi.org/10.1038/nsmb.1992

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