This study uses µMap photoproximity labeling with a small Ir catalyst to map and compare monomeric and fibrillar α‑synuclein interactomes in mouse brain lysate and neurons, identifying region-specific protein associations and validating selected hits with biochemical and imaging methods.

The method enables high-resolution, minimally perturbing identification of α‑synuclein loss- and gain-of-function interactors, which can reveal mechanistic targets and biomarkers relevant to Parkinson's therapeutic discovery.

Fibrillar aggregates of the natively disordered protein α-synuclein (αS) are hallmarks of Parkinson's disease and related neurodegenerative disorders termed synucleinopathies. Here, we used micromap (μMap) photoproximity labeling to determine the interactomes of αS monomers and fibrils in mouse brain lysate to better understand both the loss of healthy function and gain of toxic function aspects of synucleinopathies. Several αS variants were synthesized and characterized, showing that the small size (1 kDa) of the Ir catalyst attached through a Cys-maleimide linkage makes it minimally perturbing to αS, with a narrow labeling radius that allows one to identify interactome differences between different regions of αS. Monomer and fibril interactomes were compared to each other and to previous proximity labeling data sets for validation, and several examples of further investigations are demonstrated, including Western blotting, affinity pulldowns, fluorescence and super-resolution microscopy, and μMap in primary neurons.