Updated project metadata. Parkinson’s disease (PD) is a neurodegenerative disorder associated with the accumulation of intraneuronal protein aggregates called Lewy bodies. These inclusions contain aberrantly folded and aggregated alpha-synuclein (aSyn), a key protein involved in the pathology of PD, for which the mechanisms of toxicity are still largely unknown. Recent studies suggest that the conformational changes occurring during aSyn aggregation process can be expected to lead to alterations in the interactome of aSyn. Therefore, identifying changes in the interactome of monomeric and aggregated states of aSyn could help to understand the underlying molecular mechanisms of PD. Despite substantial efforts, current interactomics approaches do not enable determining structure-specific PPIs and their interaction interfaces on a proteome-wide scale. To address this limitation, we here applied the structural proteomics method limited proteolysis–mass spectrometry to systematically identify structure-specific PPIs of aSyn by probing protein structural alterations within cellular extracts upon treatment with monomeric and aggregated, fibrillar states of aSyn. Overall, we identified several previously known interactors of both monomeric and aggregated aSyn as well as novel putative structure-specific interactors including their interaction interfaces and protein binding parameters in situ. These results may constitute an important step in the understanding of how distinct structural states of disease-associated proteins are involved in disease mechanisms.