Sulfated Polysaccharides as a Fighter with Protein Non-Physiological Aggregation: The Role of Polysaccharide Flexibility and Charge Density

Abstract

Proteins can lose native functionality due to non-physiological aggregation. In this work, we have shown the power of sulfated polysaccharides as a natural assistant to restore damaged protein structures. Protein aggregates enriched by cross-β structures are a characteristic of amyloid fibrils related to different health disorders. Our recent studies demonstrated that model fibrils of hen egg white lysozyme (HEWL) can be disaggregated and renatured by some negatively charged polysaccharides. In the current work, using the same model protein system and FTIR spectroscopy, we studied the role of conformation and charge distribution along the polysaccharide chain in the protein secondary structure conversion. The effects of three carrageenans (κ, ι, and λ) possessing from one to three sulfate groups per disaccharide unit were shown to be different. κ-Carrageenan was able to fully eliminate cross-β structures and complete the renaturation process. ι-Carrageenan only initiated the formation of native-like β-structures in HEWL, retaining most of the cross-β structures. In contrast, λ-carrageenan even increased the content of amyloid cross-β structures. Furthermore, κ-carrageenan in rigid helical conformation loses its capability to restore protein native structures, largely increasing the amount of amyloid cross-β structures. Our findings create a platform for the design of novel natural chaperons to counteract protein unfolding.

Keywords: amyloid fibrils; chaperons; disaggregation effect; hen egg white lysozyme; protein renaturation; sulfated polysaccharides.

Figure 1

Structural scheme of sulfated polysaccharides used.

Figure 2

Absorbance (A) and second derivative (B) spectra of HEWL fibrils (dashed line) and their gel-like complexes with κ-carrageenan at polysaccharide/protein ratios of 0.1 (red), 0.3 (black) and 0.6 (blue). (C) Spectra of gel-like complexes of HEWL fibrils with κ-carrageenan (black) and native HEWL/κ-carrageenan complexes at a polysaccharide/protein ratio of 0.3 (dark green line and dots).

Figure 3

Second derivative spectra of HEWL fibrils (dashed line) and of their gel-like complexes with carrageenans at a polysaccharide-to-protein ratio of 0.3: (A) coiled κ- (blue line with symbols), ι- (red line) and λ- (green line) carrageenans, (B) κ-carrageenan in helical conformation (red line).

Figure 4

Correlation between the ratio of integral absorptions at 1625 and 1655 cm⁻¹ of components of the Amide I band of HEWL in complex with carrageenans, differing in number of sulfate groups per disaccharide: κ- (1), ι- (2) and λ- (3). The ratio for pure amyloid fibrils is given at X = 0 and is marked a by horizontal line.

Figure 5

Second derivative spectra of HEWL fibrils (dashed line) and of their gel-like complexes with chondroitin-4-sulfate (red line) at a polysaccharide-to-protein ratio of 0.3.