Recent research indicates that the progression of Parkinson's disease can start from neurons of the enteric nervous system, which are in close contact with the gastrointestinal epithelium: alpha-synuclein molecules can be transferred from these epithelial cells in a prion-like fashion to enteric neurons. Thin mucus layers constitute a defense line against the exposure of noninfected cells to potentially harmful alpha-synuclein species. We show that-despite its mucoadhesive properties-alpha-synuclein can translocate across mucin hydrogels, and this process is accompanied by structural rearrangements of the mucin molecules within the gel. Penetration experiments with different alpha-synuclein variants and synthetic peptides suggest that two binding sites on alpha-synuclein are required to accomplish this rearrangement of the mucin matrix. Our results support the notion that the translocation of alpha-synuclein across mucus barriers observed here might be a critical step in the infection of the gastrointestinal epithelium and the development of Parkinson's disease.