Functional interactions as a survival strategy against abnormal aggregation.
Protein aggregation is under intense scrutiny because of its role in human disease. Although increasing evidence indicates that protein native states are highly protected against aggregation, the specific protection mechanisms are poorly understood. Insight into such mechanisms can be gained through study of the relatively few proteins that aggregate under native conditions. Ataxin-3, the protein responsible for Spinocerebellar ataxia type 3, a polyglutamine expansion disease, represents one of such examples. Polyglutamine expansion is central for determining solubility and aggregation rates of ataxin-3, but these properties are profoundly modulated by its N-terminal Josephin domain. This work aims at identifying the regions that promote Josephin fibrillogenesis and rationalizing the mechanisms that protect Josephin and nonexpanded ataxin-3 from aberrant aggregation. Using different biophysical techniques, aggregation propensity predictions and rational design of amino acid substitutions, we show that Josephin has an intrinsic tendency to fibrillize under native conditions and that fibrillization is promoted by two solvent-exposed patches, which are also involved in recognition of natural substrates, such as ubiquitin. Indeed, designed mutations at these patches or substrate binding significantly reduce Josephin aggregation kinetics. Our results provide evidence that protein nonpathologic function can play an active role in preventing aberrant fibrillization and suggest the molecular mechanism whereby this occurs in ataxin-3.
Masino
Laura
L
MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK.
Nicastro
Giuseppe
G
Calder
Lesley
L
Vendruscolo
Michele
M
Pastore
Annalisa
A
D000595:Amino Acid Sequence; D000818:Animals; D000067699:Ataxin-3; D001665:Binding Sites / Q000235:genetics; D006801:Humans; D007700:Kinetics; D017827:Machado-Joseph Disease / Q000235:genetics / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008854:Microscopy, Electron; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D019680:Trinucleotide Repeat Expansion / Q000235:genetics; D025801:Ubiquitin / Q000737:chemistry / Q000378:metabolism
D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D012097:Repressor Proteins; D025801:Ubiquitin; C097188:polyglutamine; C092341:ATXN3 protein, human; D000067699:Ataxin-3
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