The intracellular misfolding and accumulation of alpha-synuclein into structures collectively called LP is a central phenomenon for the pathogenesis of synucleinopathies including Parkinson’s disease (PD) and Dementia with Lewy Bodies (DLB). Understanding the molecular architecture of LP is crucial for understanding synucleinopathy disease origins and progression. Here we used a technique called biotinylation by antibody recognition (BAR) to label total (BAR-SYN1) and pathological alpha-synuclein (BAR-PSER129) in situ for subsequent mass spectrometry analysis. This technique has broad potential to help understand the phenomenon of LP in primary human tissue and animal models.