Hydrogen Bonding and Solvation of a Proline-Based Peptide Model in Salt Solutions

Amyloidogenic and non-amyloidogenic molten globule conformation of β-lactoglobulin in self-crowded regime

Molecular insights on the β-lactoglobulin thermal unfolding and aggregation are derived from FTIR and UV Resonance Raman (UVRR) investigations. We propose an in situ and in real-time approach that thanks to the identification of specific spectroscopic markers can distinguish the two different unfolding pathways pursued by β-lactoglobulin during the conformational transition from the folded to the molten globule state, as triggered by the pH conditions. For both the investigated pH values (1.4 and 7.5) the greatest conformational variation of β-lactoglobulin occurs at 80 °C and a high degree of structural reversibility after cooling is observed. In acidic condition β-lactoglobulin exposes to the solvent its hydrophobic moieties in a much higher extent than in neutral solution, resulting on a highly open conformation. Moving from the diluted to the self-crowded regime, the solution pH and consequently the different molten globule conformation select the amyloid or non-amyloid aggregation pathway. At acidic condition the amyloid aggregates form during the heating cycle leading to the formation of transparent hydrogel. On the contrary, in neutral condition the amyloid aggregates never form. Information on the secondary structure conformational change of β-lactoglobulin and the formation of amyloid aggregates are obtained by FTIR spectroscopy and are related to the information of the structural changes localized around the aromatic amino acid sites by UVRR technique. Our results highlight a strong involvement of the chain portions where tryptophan is located on the formation of amyloid aggregates.

Amide Spectral Fingerprints are Hydrogen Bonding-Mediated

The origin of the peculiar amide spectral features of proteins in aqueous solution is investigated, by exploiting a combined theoretical and experimental approach to study UV Resonance Raman (RR) spectra of peptide molecular models, namely N-acetylglycine-N-methylamide (NAGMA) and N-acetylalanine-N-methylamide (NALMA). UVRR spectra are recorded by tuning Synchrotron Radiation at several excitation wavelengths and modeled by using a recently developed multiscale protocol based on a polarizable QM/MM approach. Thanks to the unparalleled agreement between theory and experiment, we demonstrate that specific hydrogen bond interactions, which dominate hydration dynamics around these solutes, play a crucial role in the selective enhancement of amide signals. These results further argue the capability of vibrational spectroscopy methods as valuable tools for refined structural analysis of peptides and proteins in aqueous solution.