Hypothesis

Redox‑dependent sulfonylation converts chaperone‑rich, reversible aggregates into irreversible, protease‑resistant deposits by perturbing liquid‑liquid phase separation.

Mechanistic basis

• Oxidative stress ages cysteines to sulfinic/sulfonic forms (R‑SO₂H/R‑SO₃H).
• These modifications increase hydrophobicity and charge, promoting aberrant LLPS that bypasses normal chaperone buffering (4).
• In young or long‑lived cells, low sulfonylation allows transient sequestration of misfolded proteins into JUNQ/IPOD‑like condensates that remain reversible and chaperone‑enriched (2).
• With age, rising sulfonylation tips the equilibrium toward static, amyloid‑like cores that titrate Hsp70/Hsp90 and lose antimicrobial or signaling functions (5).

Novel insight

We propose that sulfonylated aggregates act as a redox sink: they deliberately incorporate oxidized cysteines to spare the rest of the proteome from further damage. When the sink overflows, the aggregate becomes pathological. Thus, enhancing the cellular capacity to reduce sulfonylated cysteines (e.g., via sulfiredoxin/Srx or peroxiredoxin/Prx pathways) should dissolve pathological deposits without harming the protective sequestration function.

Testable predictions

1. Biochemical – In vitro, recombinant tau or p53 treated with H₂O₂ will show increased sulfonylation (detected by anti‑SO₂H/SO₃H antibodies) and form ThT‑positive aggregates that are resistant to protease K; pre‑incubation with recombinant Srx will reduce sulfonylation and restore protease sensitivity and chaperone binding (7).
2. Cellular – C. elegans strains overexpressing Srx will exhibit lower insoluble protein fractions, retain chaperone enrichment in aggregates, and show delayed onset of paralysis in Aβ models compared with wild‑type (6).
3. Therapeutic – Small‑molecule activators of the Srx pathway (e.g., mizoribine analogs) will reduce lipofuscin accumulation in microglial cultures exposed to myelin debris and improve phagocytic clearance (8).
4. Clinical relevance – Post‑mortem Alzheimer’s brain tissue will display a gradient: peripheral cortical regions with lower sulfonylation show chaperone‑rich aggregates, while dense plaques exhibit high sulfonylation and minimal Hsp70 co‑localization; immunofluorescence for SO₂H/SO₃H will inversely correlate with soluble oligomer levels.

Falsifiability

If augmenting sulfonylation reduction fails to decrease protease‑resistant aggregates or does not improve chaperone association across multiple models, the hypothesis that sulfonylation drives the protective‑to‑pathological switch is refuted. Conversely, observing that sulfonylation levels remain unchanged while aggregates transition from reversible to irreversible would also falsify the proposed redox sink mechanism.

Implications

Viewing aggregation as a regulated redox buffer reframes therapeutic strategies: instead of indiscriminately dissolving aggregates, we aim to tune the oxidation state of their constituent cysteines, preserving the cell’s last attempt at order while preventing overload.