Design of Ig-like binders targeting α-synuclein fibril for mitigating its pathological activities.

Parkinson's disease (PD) is characterized by the accumulation and spread of pathological α-synuclein (α-syn) fibrils, which contribute to neuroinflammation and neurodegeneration. Here we show that two immunoglobulin-like (Ig-like) domains derived from α-syn receptors, the D1 domain of lymphocyte-activation gene 3 (L3D1) and the V domain of advanced glycation end-products (vRAGE), effectively block cell surface binding of α-syn fibrils, suppress fibrils-induced neuronal α-syn aggregation, and reduce inflammatory responses in microglia. Building on this, we identified two additional Ig-like binders, the D1 domain of cluster of differentiation 4 (CD4 D1) and the D1 domain of chimeric antigen receptor (CAR D1), that target the C-terminal region of α-syn fibrils and mitigate fibrils-induced pathological activities. A structure-guided mutant, CAR D1_Mut, exhibits enhanced binding affinity and functional efficacy. These findings highlight the potential of Ig-like binders as molecular tools to interfere with pathological α-syn interactions.