α-Synuclein (α-Syn) is a neuronal protein associated with Parkinson’s disease that has an N-terminal lipid-binding motif and a disordered C-terminal tail. It has been previously demonstrated that α-syn can bind and remodel membranes composed of zwitterionic and anionic phospholipids; however, there has been little consideration for the role of lipid phase in binding preference. We provide evidence through circular dichroism (CD) and steady-state fluorescence experiments with tryptophan mutants that α-syn binds preferentially to the gel phase of zwitterionic small unilamellar vesicles (SUVs) composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). For DPPC, it can be clearly seen that α-syn transitions from an α-helical to a disordered conformation at the lipid’s theoretical melting temperature (Tm) of 41 °C, which was independently verified using differential scanning calorimetry. Contrastingly, in the presence of anionic SUVs composed of 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG), α-syn favors the fluid phase. To understand which regions of α-syn are essential for binding and fluidity sensing, we used two known homologs, β-syn and γ-syn, which have been independently linked to diseases such as dementia with Lewy bodies and breast carcinomas, respectively. While their sequences are highly conserved in the N-terminus, β-syn lacks 11 residues (73–83) in the central region and γ-syn has a truncated C-terminus compared to α-syn. Interestingly, both β-syn and γ-syn appear to have similar fluidity sensing capabilities as α-syn, but γ-syn binds significantly weaker to vesicles compared to both α-syn and β-syn. These results suggest that the C-terminus may play a larger role in modulating α-syn–lipid interactions than previously assumed, and offer new insights into the mechanism of α-syn lipid binding and fluidity sensing.

Membrane binding and fluidity sensing by α-, β-, and γ-synuclein

254th National Meeting (2017)

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