Disulfide Bonds Reduce the Toxicity of the Amyloid Fibrils Formed by an Extracellular Protein

Abstract

The misfolding of proteins into amyloid fibrils constitutes the hallmark of many diseases. [1] Although relatively few physicochemical properties of protein sequences-charge, hydrophobicity, patterns of polar and nonpolar residues, and tendency to form secondary structures-are sufficient to rationalize in general terms their relative propensities to form amyloid fibrils, [2,3] other properties can also be important. One example is intramolecular disulfide bonds, which limit the ways in which a polypeptide can be arranged in a fibril through the topological restraints that they impose. Although disulfide bonds are present in 15 % of the human proteome, in 65 % of secreted proteins, and in more than 50 % of those involved in amyloidosis, our understanding of how they influence the properties of amyloid fibrils is limited. [4][5][6] We have examined the formation of fibrils by human lysozyme [7,8] in the presence and absence (Figure 1 a,b) of its native disulfide bonds, and found that they profoundly influence the fibrillar morphology and cytotoxicity.

Association Between Foldability and Aggregation Propensity in Small Disulfide-Rich Proteins

“…This is likely the underlying reason explaining why, as a trend, globular proteins with disulfides bonds tend to display more aggregation-prone sequences than proteins devoid of this bond (63). Our results indicate that this generic strategy is not enough, or is not acting, to ensure the solubility of DRDs, as their sequences seem to be shaped to exhibit low aggregation propensity and a reduced number of APRs despite being enriched in disulfides and highly stable in the oxidized state.…”

Contribution of Disulfide Bonds to Stability, Folding, and Amyloid Fibril Formation: The PI3-SH3 Domain Case

“…Prevention of protein aggregation is an important selective pressure acting on the evolution of protein sequences (11); the protective effect of disulfide bonds against toxic protein deposition in the oxidative extracellular background might explain why the sequences of secreted SH3 domains can support a higher intrinsic aggregation load than those of their less stable intracellular counterparts. Importantly, during the revision of this work, a study by Mossuto et al showed that reduction of disulfides in human lysozyme increases the toxicity of the resulting fibrils and, more generally, that disulfidecontaining proteins in the human proteome display a high aggregation propensity (36). Overall, it appears that the impact that covalent polypeptide crosslinking exerts in the complex processes of protein folding and aggregation might be more relevant from the physiological point of view than previously thought.…”

Inhibition of amyloid fibrillation of lysozyme by phenolic compounds involves quinoprotein formation

“…Under in vitro conditions of low pH and elevated temperature, lysozyme is able to transform into amyloid fibrils with typical fibrillar morphology and increased binding capacities for ThT and Congo Red [5]. Recent investigations showed that the synthetic lysozyme fibrils exhibited non-enzymatic cytotoxicity, including inducing aggregation and hemolysis of human erythrocytes, triggering intermolecular cross-linking of cytoskeletal proteins and reducing the viability of neuroblastoma cells through apoptotic and necrotic pathways [6][7][8].…”