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

Molecular insights on the beta-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 beta-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 beta-lactoglobulin occurs at 80 degrees C and a high degree of structural reversibility after cooling is observed. In acidic condition beta-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 beta-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.

Automated summary

Molecular insights on the thermal unfolding and aggregation of beta-lactoglobulin were obtained using FTIR and UV Resonance Raman investigations. A new in situ and in real-time approach was proposed to distinguish the two unfolding pathways of beta-lactoglobulin under different pH conditions. The conformational change of beta-lactoglobulin and the formation of amyloid aggregates were studied using FTIR spectroscopy and UVRR technique. The results revealed the importance of tryptophan-containing regions in the formation of amyloid aggregates.