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

Scirè, Andrea, Baldassarre, Maurizio, Tanfani, Fabio, Capraro, Jessica, Duranti, Marcello, Scarafoni, Alessio
Biochimica et biophysica acta 2018 v.1866 no.12 pp. 1242-1248
Fourier transform infrared spectroscopy, Lupinus albus, dihydroxyphenylalanine, models, oligomerization, phospholipids, seeds, solvents, thermal stability, turbidity
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 p²H 7.0 and at p²H 4.5. The protein maintains the same secondary structure both at p²H 7.0 and at p²H 4.5, but at p²H 7.0 a higher ¹H/²H exchange was observed, indicating a greater solvent accessibility. The difference in Tm and TD1/2 of the protein at the abovementioned p²H's has been calculated around 20 °C. Infrared measurements have been then performed in the presence of DMPG and DOPA at p²H 4.5. DMPG showed a little destabilizing effect while DOPA exerted a great stabilizing effect, increasing the Tm of γ-conglutin at p²H 4.5 of more than 20 °C. Since γ-conglutin at p²H 4.5 is in the monomeric form, the interaction with DOPA likely promotes the oligomerization even at p²H 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.