Brain Metabolite, N-Acetylaspartate Is a Potent Protein Aggregation Inhibitor

Abstract

Deposition of toxic protein inclusions is a common hallmark of many neurodegenerative disorders including Alzheimer's disease, Parkinson disease etc. N-acetylaspartate (NAA) is an important brain metabolite whose levels got altered under various neurodegenerative conditions. Indeed, NAA has been a widely accepted biological marker for various neurological disorders. We have also reported that NAA is a protein stabilizer. In the present communication, we investigated the role of NAA in modulating the aggregation propensity on two model proteins (carbonic anhydrase and catalase). We discovered that NAA suppresses protein aggregation and could solubilize preformed aggregates.

Keywords: light scattering; neurological disorders; protein aggregation; protein denaturation; protein stability.

Figure 1

Time dependent aggregation profiles of carbonic anhydrase. (A) Aggregation kinetics of CA monitored by observing changes in the light scattering intensity at 500 nm in presence and absence of NAA. The lines present the best fits of the data using Equation (1). Results shown are representative of at least three independent measurements and mean error of the best fits are given in Table 1. (B) Plots of I_f vs. NAA concentrations. Error bars represents the standard errors of the mean. (C) Transmission electron microscopy images of CA in absence of NAA (left panel) and in presence (right panel) of 1 M NAA.

Figure 2

Time dependent aggregation profiles of catalase. Aggregation kinetics of catalase monitored by observing changes in the light scattering intensity at 360 nm in presence and absence of NAA. The lines present the best fits of the data using Equation (1). Results shown are representative of at least three independent measurements and mean error of the three independent best fits are given in Table 2.

Figure 3

Temperature dependent aggregation profiles of carbonic anhydrase. (A) Temperature dependent aggregation kinetics of CA monitored by observing changes in the light scattering intensity at 500 nm in presence and absence of NAA. The lines present the best fits of the data using Equation (2). Results shown are representative of at least three independent measurements and mean error of the three independent best fits are given in Table 3. (B) Plots of T_agg vs. lag time.

Figure 4

Urea denaturation profiles of CA. Denaturation of CA by observing changes at 355 nm using different concentration of urea in presence and absence of NAA. Excitation wavelength was 280 nm. Results shown are representative of at least three independent measurements and mean error of the three independent best fits are given in Table 4.

Figure 5

Effect of NAA on native state conformation of CA. (A) Near UV-CD spectra (tertiary structure) of CA in absence and presence of NAA (B) Intrinsic fluorescence emission spectra of CA in absence and presence of NAA (C) ANS emission fluorescence spectra of CA. The spectra shown are representative of three independent measurements.

Figure 6

NAA effect on reversing preformed CA aggregates. (A) Light scattering intensities of aggregated CA in the presence of different NAA concentrations (B) Intensities upon prolong incubations in presence of 1.0 M NAA. Error bars represent standard error of the mean.