title: Huntingtin fragments and SOD1 mutants form soluble oligomers in the cell.
abstract: Diffusion coefficients of huntingtin (Htt) fragments and SOD1 mutants expressed in cells were measured using fluorescence correlation spectroscopy. The diffusion mobilities of both non-pathological Htt fragments (25 polyQs) and pathological Htt fragments (103 polyQs) were much slower than expected for monomers suggesting that they oligomerize. The mobility of these fragments was unaffected by duration of expression or by over-expression of Hsp70 and Hsp40. However in cells with HttQ103 inclusions, diffusion measurements showed that the residual cytosolic HttQ103 was monomeric. These results suggest that both non-pathological and pathological Htt fragments form soluble oligomers in the cytosol with the properties of the oligomers determining whether they cause pathology. SOD1 with point mutations (A4V, G37R, and G85R) also had slower diffusional mobility than the wild-type protein whose mobility was consistent with that of a dimer. However, the decrease in mobility of the different SOD1 mutants did not correlate with their known pathology. Therefore, while soluble oligomers always seem to be present under conditions where cell pathology occurs, the presence of the oligomers, in itself, does not determine the extent of neuropathology.
authors: Laboratory of Cell Biology, National Heart Lung Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
authors: Yang-Nim
authors: YN
authors: Park
authors: Xiaohong
authors: X
authors: Zhao
authors: Mark
authors: M
authors: Norton
authors: J Paul
authors: JP
authors: Taylor
authors: Evan
authors: E
authors: Eisenberg
authors: Lois E
authors: LE
authors: Greene
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002457:Cell Extracts; D004058:Diffusion; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D050505:Mutant Proteins / Q000737:chemistry* / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D017354:Point Mutation / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors / Q000494:pharmacology; D020836:Protein Structure, Quaternary; D012995:Solubility; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000378:metabolism*; D000072105:Superoxide Dismutase-1; D013997:Time Factors; D014162:Transfection
chemical_list: D002457:Cell Extracts; D050505:Mutant Proteins; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D010455:Peptides; D061988:Proteasome Inhibitors; C000606290:SOD1 protein, human; D049452:Green Fluorescent Proteins; C097188:polyglutamine; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D046988:Proteasome Endopeptidase Complex