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

Interaction with model phospholipid membranes of lupin seed gamma-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 H-1/H-2 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 degrees 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 gamma-conglutin at p(2)H 4.5 of more than 20 degrees C. Since gamma-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 gamma-conglutin has been confirmed by turbidity experiments with DMPC:DMPG or DOPC:DOPA SUVs. Turbidity data also showed high-affinity binding of gamma-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 gamma-conglutin.