Interaction of γ-conglutin from Lupinus albus with model phospholipid membranes: Investigations on structure, thermal stability and oligomerization status

Abstract Interaction with model phospholipid membranes of lupin seed γ-conglutin, a glycaemia-lowering protein from Lupinus albus seeds, has been studied by means of Fourier-Transform infrared spectroscopy at p 2 H 7.0 and at p 2 H 4.5. The protein maintains the same secondary structure both at p 2 H 7.0 and at p 2 H 4.5, but at p 2 H 7.0 a higher 1 H/ 2 H exchange was observed, indicating a greater solvent accessibility. The difference in T m and T D1/2 of the protein at the abovementioned p 2 H's has been calculated around 20 °C. Infrared measurements have been then performed in the presence of DMPG and DOPA at p 2 H 4.5. DMPG showed a little destabilizing effect while DOPA exerted a great stabilizing effect, increasing the T m of γ-conglutin at p 2 H 4.5 of more than 20 °C. Since γ-conglutin at p 2 H 4.5 is in the monomeric form, the interaction with DOPA likely promotes the oligomerization even at p 2 H 4.5. Interaction between DMPG or DOPA and γ-conglutin has been confirmed by turbidity experiments with DMPC:DMPG or DOPC:DOPA SUVs. Turbidity data also showed high-affinity binding of γ-conglutin to anionic SUVs made up with DOPA. The molecular features outlined in this study are relevant to address the applicative exploitation and to delineate a deeper comprehension of the natural functional role of γ-conglutin.