# Differences in α-synuclein conformational states in physiologically relevant pH/Na+ concentrations and ammonium acetate solutions unveiled by native mass spectrometry

## TL;DR

This study uses mass spectrometry to show how α-synuclein proteins change shape in different salt and pH conditions, which may relate to disease processes.

## Contribution

The study reveals new insights into α-synuclein conformational flexibility under physiological conditions using native mass spectrometry with theta emitters.

## Key findings

- α-synuclein shows high conformational flexibility at 150 mM NaCl and pH 7.4.
- At acidic pH, the protein adopts less compact conformations influenced by Na+.
- Oligomer formation varies by protein type, with wild-type forming dimers and truncated forming larger oligomers.

## Abstract

Native mass spectrometry implemented with theta emitters was used to demonstrate differences in conformational states of wild-type, A53T mutant, and truncated α-synuclein dissolved at physiologically relevant pH and Na+ concentrations compared to aqueous solutions of ammonium acetate. Specifically, 150 mM NaCl at pH 7.4, 20 mM NaCl at pH 4.5, and 15 mM NaCl at pH 7.2 were used to reflect, to some extent, the extracellular environment, lysosome, and cytosol, respectively. Analysis of charge state distributions obtained from physiologically relevant solutions vs. their ammonium acetate counterparts allows the comparison of α-synuclein conformational states. The protein shows relatively high conformational flexibility at 150 mM NaCl and pH 7.4, while it shows at least two different conformational states at 20 mM NaCl and pH 4.5. We observed a trend towards the adoption of less compact conformations at acidic pH, where Na+ appears to play a distinctive role in the adoption of different conformational states. Early-stage oligomers (dimer, pentamer, hexamer and heptamer) were also detected. Since oligomer formation was protein-specific, wild-type α-synuclein formed dimers while truncated α-synuclein formed pentamers, hexamers and heptamers, their abundances are consistent with kinetics of aggregation reported in the literature.

Native MS implemented with theta emitters was used to demonstrate differences in conformational states of wild-type and mutant α-synuclein dissolved at physiologically relevant pH and Na+ concentrations compared to solutions of ammonium acetate.