DIBMA nanodiscs keep α-synuclein folded

alpha-Synuclein (alpha syn) is a cytosolic intrinsically disordered protein (IDP) known to fold into an alpha-helical structure when binding to membrane lipids, decreasing protein aggregation. Model membrane enable elucidation of factors critically affecting protein folding/aggregation, mostly using either small unilamellar vesicles (SUVs) or nanodiscs surrounded by membrane scaffold proteins (MSPs). Yet SUVs are mechanically strained, while MSP nanodiscs are expensive. To test the impact of lipid particle size on alpha-syn structuring, while overcoming the limitations associated with the lipid particles used so far, we compared the effects of large unilamellar vesicles (LUVs) and lipid-bilayer nanodiscs encapsulated by diisobutylene/maleic acid copolymer (DIBMA) on alpha syn secondary-structure formation, using human-, elephant- and whale -alpha syn. Our results confirm that negatively charged lipids induce alpha syn folding in h-alpha syn and e-alpha syn but not in w-alpha syn. When a mixture of zwitterionic and negatively charged lipids was used, no increase in the secondary structure was detected at 45 degrees C. Further, our results show that DIBMA/lipid particles (DIBMALPs) are highly suitable nanoscale membrane mimics for studying alpha syn secondary-structure formation and aggregation, as folding was essentially independent of the lipid/protein ratio, in contrast with what we observed for LUVs having the same lipid compositions. This study reveals a new and promising application of polymer-encapsulated lipid-bilayer nanodiscs, due to their excellent efficiency in structuring disordered proteins such as alpha syn into nontoxic alpha-helical structures. This will contribute to the unravelling and modelling aspects concerning protein-lipid interactions and alpha-helix formation by alpha syn, paramount to the proposal of new methods to avoid protein aggregation and disease.