Effect of disease-associated P123H and V70M mutations on β-synuclein fibrillation.

Synucleinopathies are a class of neurodegenerative diseases, including Parkinson's disease (PD), Dementia with Lewy bodies (DLB), and Multiple System Atrophy (MSA). The common pathological hallmark of synucleinopathies is the filamentous alpha-synuclein (alpha-Syn) aggregates along with membrane components in cytoplasmic inclusions in the brain. beta-Synuclein (beta-Syn), an isoform of alpha-Syn, inhibits alpha-Syn aggregation and prevents its neurotoxicity, suggesting the neuroprotective nature of beta-Syn. However, this notion changed with the discovery of disease-associated beta-Syn mutations, V70M and P123H, in patients with DLB. It is still unclear how these missense mutations alter the structural and amyloidogenic properties of beta-Syn, leading to neurodegeneration. Here, we characterized the biophysical properties and investigated the effect of mutations on beta-Syn fibrillation under different conditions. V70M and P123H show high membrane binding affinity compared to wild-type beta-Syn, suggesting their potential role in membrane interactions. beta-Syn and its mutants do not aggregate under normal physiological conditions; however, the proteins undergo self-polymerization in a slightly acidic microenvironment and/or in the presence of an inducer, forming long unbranched amyloid fibrils similar to alpha-Syn. Strikingly, V70M and P123H mutants exhibit accelerated fibrillation compared to native beta-Syn under these conditions. NMR study further revealed that these point mutations induce local perturbations at the site of mutation in beta-Syn. Overall, our data provide insight into the biophysical properties of disease-associated beta-Syn mutations and demonstrate that these mutants make the native protein more susceptible to aggregation in an altered microenvironment.