No abstract

Synthetic peptides are widely used to understand the protein misfolding and aggregation observed in a diverse group of diseases called systemic amyloidosis and neurodegenerative disorders. The preparation of monomeric solutions of the aggregation‐prone peptides is necessary for achieving a mechanistic understanding efficiently, without compromising any critical step. This study describes novel approaches and mechanisms behind the conversion of otherwise insoluble/sparingly soluble peptides to soluble monomers by trifluoroacetic acid and hexafluoroisopropanol. Although the pretreatment with these solvents results in more or less similar monomers, the mechanism followed to achieve this differs with the solvent. Data show that these solvents aid in the solubility by disrupting the extensive intramolecular and/or intermolecular H‐bond network present in the insoluble peptides.

The data provided in this article are related to the research article entitled “Unaided trifluoroacetic acid pretreatment solubilizes polyglutamine (polyGln) peptides and retains their biophysical properties of aggregation” by Burra and Thakur (in press) [1]. This research article reports data from size exclusion chromatography (SEC), reversed phase-high performance liquid chromatography (RP-HPLC) and mass spectrometry (MS) assays. This data show that trifluoroacetic acid (TFA) has the ability to convert insoluble polyGln peptides to soluble monomers. The data also clarify the possibility of trifluoroacetylation modification caused due to TFA. We hope the data presented here will enhance the understanding of polyGln disaggregation and solubilization. For more insightful and useful discussions, see the research article published in Analytical Biochemistry: Methods in the Biological Sciences (Burra and Thakur, in press [1]).

Dityrosine (DiY), via the cross-linking of tyrosine residues, is a marker of protein oxidation, which increases with aging. Amyloid-b (Ab) forms DiY in vitro and DiYcross-linked Ab is found in the brains of patients with Alzheimer disease. Metal-or UV-catalyzed oxidation of Ab42 results in an increase in DiY cross-links. Using DiY as a marker of oxidation, we compare the self-assembly propensity and DiY crosslink formation for a non-assembly competent variant of Ab42 (vAb) with wildtype Ab42. Oxidation results in the formation of trapped wild-type Ab assemblies with increased DiY cross-links that are unable to elongate further. Assemblyincompetent vAb and trapped Ab assemblies are non-toxic to neuroblastoma cells at all stages of self-assembly, in contrast to oligomeric, non-cross-linked Ab. These findings point to a mechanism of toxicity that necessitates dynamic self-assembly whereby trapped Ab assemblies and assembly-incompetent variant Ab are unable to result in cell death.

The mutant huntingtin protein (mHtt) fragments with expanded polyglutamine sequence forms microscopically visible aggregates in neurons, a hallmark of Huntington's disease (HD). The aggregation process and aggregates are possible targets of therapeutic intervention in HD. Owing to the lack of treatment and cure, the patients die within 15-20 years after the disease onset. Therefore, discovering therapeutic molecules that may either inhibit the aggregation mechanism or downregulate the toxic effects of mHtt are highly needed. This study demonstrates the design and use of peptide inhibitors based on the role played by the N-terminal seventeen amino acid sequence (NT ) of huntingtin fragment in its aggregation. Fug-NT (Fugu), Xen-NT (Xenopus), Dro-NT (Drosophila), Aib-NT , and Pro-NT sequences were tested for their ability to inhibit aggregation. Among them, the first three are the sequence variants of human NT from evolutionarily distant organisms and the latter two are the analogs of human NT -containing aminoisobutyric acid (Aib) and proline (Pro). Four out of five inhibited the aggregation of huntingtin fragment, NT Q P K polypeptide. Data indicate that the physicochemical properties of the inhibitors play a crucial role in exhibiting the inhibitory effect. These inhibitors can be tested in cell and animal models for the preclinical evaluation in the treating of HD.