Membrane Remodeling by α-Synuclein and Effects on Amyloid Formation

Abstract

α-Synuclein (α-Syn), an intrinsically disordered protein, is associated with Parkinson’s disease. Though molecular pathogenic mechanisms are ill-defined, mounting evidence connects its amyloid forming and membrane binding propensities to disease etiology. Contrary to recent data suggesting that membrane remodeling by α-syn involves anionic phospholipids and helical structure, we discovered that the protein deforms vesicles with no net surface charge (phosphatidylcholine, PC) into tubules (average diameter ~ 20 nm). No discernible secondary structural changes were detected by circular dichroism spectroscopy upon the addition of vesicles. Notably, membrane remodeling inhibits α-syn amyloid formation affecting both lag and growth phases. Using five single-tryptophan variants and time-resolved fluorescence anisotropy measurements, we determined that α-syn influences bilayer structure with surprisingly weak interaction and no site specificity (partition constant, Kp ~ 300 M−1). Vesicle deformation by α-syn under a variety of different lipid/protein conditions is characterized via transmission electron microscopy. As cellular membranes are enriched in PC lipids, these results support possible biological consequences for α-syn induced membrane remodeling related to both function and pathogenesis.

Amyloidogenic Mutation Promotes Fibril Formation of the N-terminal Apolipoprotein A-I on Lipid Membranes

“…In contrast, only the 1-83/G26R variant formed ThT active, straight fibrils in the presence of excess SUV. Interestingly, the 1-83 variant appeared to cause membrane budding or tubulation of vesicles after incubation instead of fibril formation, as reported for full-length apoA-I (46) and ␣-synuclein (32,47). No fibrils were observed by TEM for the apoA-I 1-83 incubated with SUV over 240 h (data not shown).…”

Structural Features of Membrane-bound Glucocerebrosidase and α-Synuclein Probed by Neutron Reflectometry and Fluorescence Spectroscopy

“…Preparation of Lipid Vesicles for Bromine Quenching and CD Experiments-Lipid vesicles were prepared as described previously (38). For Trp penetration depth experiments, brominated phosphatidylcholine lipids (Br 6 -7 , Br 9 -10 , and Br [11][12] ) were added to a final concentration of 30% while maintaining an overall 1:1 molar ratio of phosphatidylserine and phosphatidylcholine.…”

α-Synuclein assembles into higher-order multimers upon membrane binding to promote SNARE complex formation

“…33 and 34 and Discussion for a divergent view). Membrane binding by α-synuclein is likely physiologically important because in in vitro experiments, α-synuclein remodels membranes (35,36), influences lipid packing (37,38), and induces vesicle clustering (39). Moreover, membranes were found to be important for the neuropathological effects of α-synuclein (40)(41)(42)(43)(44).…”