Polyanion binding accelerates the formation of stable and low‐toxic aggregates of ALS‐linked SOD1 mutant A4V

Abstract

The toxic property thus far shared by both ALS-linked SOD1 variants and wild-type SOD1 is an increased propensity to aggregation. However, whether SOD1 oligomers or aggregates are toxic to cells remains to be well defined. Moreover, how the toxic SOD1 species are removed from intra- and extracellular environments also needs to be further explored. The DNA binding has been shown to be capable of accelerating the aggregatio\n of wild-type and oxidized SOD1 forms under acidic and neutral conditions. In this study, we explore the binding of DNA and heparin, two types of essential life polyanions, to A4V, an ALS-linked SOD1 mutant, under acidic conditions, and its consequences. The polyanion binding alters the A4V conformation, neutralizes its local positive charges, and increases its local concentrations along the polyanion chain, which are sufficient to lead to acceleration of the pH-dependent A4V aggregation. The accelerated aggregation, which is ascribed to the polyanion binding-mediated removal or shortening of the lag phase in aggregation, contributes to the formation of amorphous A4V nanoparticles. The prolonged incubation with polyanions not only results in the complete conversion of likely soluble toxic A4V oligomers into non- and low-toxic SDS-resistant aggregates, but also increases their stability. Although this is only an initial step toward reducing the toxicity of SOD1 mutants, the accelerating role of polyanions in protein aggregation might become one of the rapid pathways that remove toxic forms of SOD1 mutants from intra- and extracellular environments.

Probing Intermolecular Interactions of Amyloidogenic Fragments of SOD1 by Site-Specific Tryptophan and Its Noncanonical Derivative

“…The misfolding and aggregation of superoxide dismutase 1 (SOD1) are associated with the fetal neurodegenerative disease amyotrophic lateral sclerosis (ALS). − Recent X-ray crystallographic studies have captured a corkscrew-like oligomeric species formed by the amyloidogenic segment residues 28–38 of SOD1 (with the sequence KVKVWGSIKGL). , This segment is the core fragment of the SOD1 protein and has been reported to play a critical role in SOD1-mediated toxicity . The physiological relevance of the oligomeric species formed by SOD1 28–38 calls for the dynamic studies to follow its evolution, which will provide important insights into the aggregation mechanism of the full-length protein. , Particularly, it is unknown whether the corkscrew-like oligomer is an on-pathway intermediate or an off-pathway by-product.…”

Haplotype Analysis of the First A4V-SOD1 Spanish Family: Two Separate Founders or a Single Common Founder?

“…There is some variability in the propensity of SOD1 mutants to aggregate, which could be related to the duration of the disease. High-aggregation propensities have been described for p.A5V, which could be the factor responsible for the disease’s short duration (Prudencio et al, 2009; Zhao et al, 2014; Farrawell et al, 2018; Maurel et al, 2018; Srinivasan and Rajasekaran, 2018).…”

Proteasome Biology: Chemistry and Bioengineering Insights

“…In this way, the polyanionic polymers may attract not only cationic substrates but also protons, resulting in a lower local pH around the enzyme. Processes such as an increase in the local concentration of a protein substrate, neutralization of its positive charges, and changes in its conformation were suggested to be driving forces behind the protein aggregation induced by polyanionic biopolymers, including heparan, anionic lipids, and nucleic acids [303,304]. In addition, local changes in pH in the proximity of the carrier (arising from such processes as the local reactions of an enzyme, partitioning effects, and diffusional limitations of H + ) can also result in a shift of the pH optimum of the immobilized enzyme.…”