N-terminal acetylation does not alter α-synuclein's interfacial properties

Alpha-synudein (alpha S) is a membrane-binding protein found predominantly in neurons and erythrocytes. The protein remains unordered in aqueous solutions but folds into an alpha-helical structure when bound to membranes. Besides, it gets deposited as beta-sheet rich aggregates in diseases known as synucleinopathies. The native alpha S has been reported to be acetylated at the N-terminus. Here, we compare the interfacial properties of the N-terminal acetylated alpha S (Ac-alpha S) with non-acetylated alpha S (NH2-alpha S) at the air-water interface. Both the protein forms are highly surface-active, with surface pressure reaching up to similar to 30 mN/m upon compression. The pressure-area isotherms obtained from the repeated compression-expansion cycles display large hysteresis suggesting self-assembly at higher surface pressures. The expansion isotherm is characterized by a rapid decrease in surface pressure followed by a slower transition phase starting around 15-17 mN/m. These data suggest that the compressed monolayer breaks into small dusters upon expansion, followed by these dusters' loosening. The circular dichroism spectroscopic analysis of the Blodgett-deposited films suggests the protein to be in largely alpha-helical conformation. The linear dichroism investigations suggest the protein to be anisotropically deposited. Blodgett deposition of the Langmuir films, therefore, is a rather simple method for preparing oriented monolayers of surface-active macromolecules. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study compared the interfacial properties of N-terminal acetylated alpha S with non-acetylated alpha S at the air-water interface, showing both protein forms to be highly surface-active and exhibit large hysteresis in pressure-area isotherms, indicating self-assembly at higher surface pressures. The expansion isotherm revealed a rapid decrease in surface pressure followed by a slower transition phase, suggesting the compressed monolayer breaks into small clusters upon expansion. The circular dichroism analysis indicated the protein to be largely in alpha-helical conformation, and linear dichroism investigations suggested anisotropic deposition of the protein.