Distinct hydration properties of wild-type and familial point mutant A53T of α-synuclein associated with Parkinson's disease

Abstract

The propensity of α-synuclein to form amyloid plays an important role in Parkinson's disease. Three familial mutations, A30P, E46K, and A53T, correlate with Parkinson's disease. Therefore, unraveling the structural effects of these mutations has basic implications in understanding the molecular basis of the disease. Here, we address this issue through comparing details of the hydration of wild-type α-synuclein and its A53T mutant by a combination of wide-line NMR, differential scanning calorimetry, and molecular dynamics simulations. All three approaches suggest a hydrate shell compatible with a largely disordered state of both proteins. Its fine details, however, are different, with the mutant displaying a somewhat higher level of hydration, suggesting a bias to more open structures, favorable for protein-protein interactions leading to amyloid formation. These differences disappear in the amyloid state, suggesting basically the same surface topology, irrespective of the initial monomeric state.

Figure 1

Temperature dependencies of hydration as measured by ¹H NMR for 25 mg·cm⁻³α-synuclein dissolved in pure water of the wild and A53T variants. The dotted line is at the hydration level 0.3 g water/g protein; solid lines are guides to the eye.

Figure 2

Temperature dependencies of hydration as measured by ¹H NMR for 50 mg·cm⁻³α-synuclein dissolved in pure water of the wild and A53T variants. The dotted line is at the hydration level 0.3 g water/g protein; solid lines are guides to the eye.

Figure 3

Comparison of the temperature dependencies of hydration as measured by ¹H NMR of the 25 mg·cm⁻³α-synuclein dissolved in pure water (wild and A53T variants) and the globular (ubiquitin and bovine serum albumin) or intrinsically disordered (ERD10) proteins. The measured data points are represented by smooth lines for the sake of clarity. The dotted line is at the hydration level 0.3 g water/g protein.

Figure 4

Comparison of the temperature dependencies of hydration as measured by ¹H NMR of α-synuclein and its amyloid dissolved in pure water (wild–type (upper) and A53T (lower); protein concentration is 25 mg·cm⁻³ in each case). The dotted line is at the hydration level 0.3 g water/g protein; solid lines serve as guides to the eye.

Figure 5

Enthalpy changes for wild-type α-synuclein, its amyloid, and the globular protein ubiquitin dissolved in pure water.

Figure 6

Molecular dynamics simulation of the hydration shell on globular domains and α-synuclein models. (A) Number of water molecules normalized to the number of residues as a function of hydration shell extent. The hydration shell was modeled using the sleap module of AmberTools on 10 selected globular domain and 101 α-synuclein structures (see Methods). The dotted line corresponds to the first hydration shell water number measured by NMR. (Inset) The first derivates of the curves. (B) Frequency distribution of the distance of water molecules (oxygen atom) from the nearest protein heavy atom in the 5-Å-extent hydration shell.