Abstract
Interactions between a solvent and their co-solute molecules in solutions of peptides are crucial for their stability and structure. The K-peptide is a synthetic fragment of a larger hen egg white lysozyme protein that is believed to be able to aggregate into amyloid structures. In this study, a complex experimental and theoretical approach is applied to study systems comprising the peptide, water, and two co-solutes: trimethylamide N-oxide (TMAO) or dimethyl sulfoxide (DMSO). Information about their interactions in solutions and on the stability of the K-peptide was obtained by FTIR spectroscopy and differential scanning microcalorimetry. The IR spectra of various osmolyte–water–model-peptide complexes were simulated with the DFT method (B3LYP/6-311++G(d,p)). The FTIR results indicate that both solutes are neutral for the K-peptide in solution. Both co-solutes affect the peptide to different degrees, as seen in the shape of its amide I band, and have different influences on its thermal stability. DFT calculations helped simplify the experimental data for easier interpretation.
Highlights
Protein or peptide aggregation is a natural phenomenon that, in certain circumstances, can be dangerous
In light of our experimental and theoretical results, we conclude that both dimethyl sulfoxide (DMSO) and trimethylamide N-oxide (TMAO) do not interact directly with the K-peptide in an aqueous solution
Some changes in the vibrational structure of both osmolytes are visible in the FTIR spectra, when the peptide is present in their solutions, they can be ascribed solely to the effect of a concentration change
Summary
Protein or peptide aggregation is a natural phenomenon that, in certain circumstances, can be dangerous. One such deleterious process is the formation of amyloid fibrils. Around 40 diseases are believed to be linked to the formation of amyloids [4], including Alzheimer’s disease, Parkinson’s disease, and type II diabetes The role of such protein assemblies in pathogenesis is unknown or even questioned. The role of aromatic AA residues is especially important [9] Keeping all of this in mind, great effort have been undertaken to identify the core part of a protein that triggers amyloidogenesis [10,11,12]
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