Stimulation of α-synuclein amyloid formation by phosphatidylglycerol micellar tubules

• Published in: Biochimica et biophysica acta. Biomembranes 2018-09, Vol.1860 (9), p.1840-1847
• Main Authors: Jiang, Zhiping, Flynn, Jessica D., Teague, Walter E., Gawrisch, Klaus, Lee, Jennifer C.
• Format: Article
• Language: English
• Subjects: Circular dichroism; Membrane remodeling; Parkinson's disease; Protein-lipid interaction; Thioflavin T; Transmission electron microscopy
• ISSN: 0005-2736; 1879-2642
• DOI: 10.1016/j.bbamem.2018.02.025

α-Synuclein (α-Syn) is a presynaptic protein that is accumulated in its amyloid form in the brains of Parkinson's patients. Although its biological function remains unclear, α-syn has been suggested to bind to synaptic vesicles and facilitate neurotransmitter release. Recently, studies have found that α-syn induces membrane tubulation, highlighting a potential mechanism for α-syn to stabilize highly curved membrane structures which could have both functional and dysfunctional consequences. To understand how membrane remodeling by α-syn affects amyloid formation, we have studied the α-syn aggregation process in the presence of phosphatidylglycerol (PG) micellar tubules, which were the first reported example of membrane tubulation by α-syn. Aggregation kinetics, β-sheet content, and macroscopic protein-lipid structures were observed by Thioflavin T fluorescence, circular dichroism spectroscopy and transmission electron microscopy, respectively. Collectively, the presence of PG micellar tubules formed at a stochiometric (L/P = 1) ratio was found to stimulate α-syn fibril formation. Moreover, transmission electron microscopy and solid-state nuclear magnetic resonance spectroscopy revealed the co-assembly of PG and α-syn into fibril structures. However, isolated micellar tubules do not form fibrils by themselves, suggesting an important role of free α-syn monomers during amyloid formation. In contrast, fibrils did not form in the presence of excess PG lipids (≥L/P = 50), where most of the α-syn molecules are in a membrane-bound α-helical form. Our results provide new mechanistic insights into how membrane tubules modulate α-syn amyloid formation and support a pivotal role of protein–lipid interaction in the dysfunction of α-syn. [Display omitted] •α-Syn remodels anionic PG, PA, and PS membranes into micellar tubules.•Effect of POPG on α-syn amyloid formation was probed by CD, ThT fluorescence, and TEM.•POPG micellar tubules shorten the lag phase and enhanced β-sheet formation.•POPG micellar tubules are co-assembled into α-syn fibrils.•POPG micellar tubes do not to convert into amyloids in the absence of free α-syn.