Amyloid-induced aggregation and precipitation of soluble proteins: an electrostatic contribution of the Alzheimer's beta(25-35) amyloid fibril.
Amyloid-induced aggregation and precipitation of soluble proteins were investigated in vitro using the amyloid fibrils of the beta(25--35) peptide, a cytotoxic fragment of the Alzheimer's beta-peptide at positions 25--35. The aggregation rate of firefly luciferase was found to be modulated by both a chaperone molecule DnaK and the beta(25--35) amyloid, but their effects were opposite in direction. The amyloid fibril drastically facilitated the luciferase aggregation, which may define a kind of anti-chaperone activity. The effect of the beta(25--35) amyloid to promote protein aggregation and precipitation was further demonstrated for a wide variety of target proteins. The amount of coprecipitation was well correlated with the predicted isoelectric point of the target proteins, indicating that the interaction between the beta(25--35) amyloid and the target was driven by an electrostatic force between them. This view was confirmed by the experiments using an electrically neutral mutant peptide, beta(25--35)KA. It was also found that clustering of the beta(25--35) peptide to form amyloid and the conformation of the target protein are additional factors that determine the strength of the amyloid-protein interaction. Spectroscopic and electron microscopic methods have revealed that the proteins coprecipitated with the beta(25--35) amyloid formed amorphous aggregates deposited together with the amyloid fibrils. The conformation of protein molecules left in the residual soluble fraction was also damaged in the amyloid-containing solution. As a summary, this study has proposed a scheme for events related to the nonspecific amyloid-protein interaction, which may play substantial roles in in vivo conditions.
Konno
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Department of Physiology, Fukui Medical University, Yoshida, Fukui, 910-1193, Japan. konno@fmsrsa.fukui-med.ac.jp
D000544:Alzheimer Disease / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D011232:Chemical Precipitation; D002942:Circular Dichroism; D001517:Coleoptera / Q000201:enzymology; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D009391:Nephelometry and Turbidimetry; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D011489:Protein Denaturation; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D012995:Solubility; D017550:Spectroscopy, Fourier Transform Infrared; D055672:Static Electricity
D016229:Amyloid beta-Peptides; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D010446:Peptide Fragments; D011506:Proteins; C074636:amyloid beta-protein (25-35); D008156:Luciferases; C063842:dnaK protein, E coli