Claudio Bussi (@claudiobussi.bsky.social)

Cathepsin-dependent amyloid formation drives mechanical rupture of lysosomal membranes Lysosomal membrane integrity is essential for cellular homeostasis, and its failure drives lysosomal storage disorders (LSD) and neurodegeneration. The dipeptide L-leucyl-L-leucine methyl ester (LLOMe) is widely used to model lysosomal damage, yet its mechanism remains poorly understood. The prevailing view holds that LLOMe polymerizes into membrane-permeabilizing peptide chains within the lysosomal lumen. Using cryo-electron tomography in cultured cells and primary neurons, we visualized the structural basis of LLOMe-induced lysosomal damage. We reveal that LLOMe forms amyloid structures within lysosomes that directly interact with and rupture the limiting membrane through mechanical stress. In vitro reconstitution confirms this amyloid-mediated mechanism. These findings establish a structural paradigm for lysosomal membrane disruption and provide insights into how disease-relevant protein aggregates, implicated in neurodegeneration and LSD, may compromise lysosomal integrity. ### Competing Interest Statement J.W.H. is a co-founder of Caraway Therapeutics, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA (Caraway) and is a scientific advisory board member for Lyterian Therapeutics. Aligning Science Across Parkinson's, https://ror.org/03zj4c476, ASAP-000350, ASAP-000282, ASAP-024268 Boehringer Ingelheim Fonds, https://ror.org/00dkye506 Deutsche Forschungsgemeinschaft, https://ror.org/018mejw64, GRK 2566/1 Pew Scholars Program NIH Common Fund, https://ror.org/001d55x84, RF1NS125674, R01NS110395 Fred and Joan Goldberg Post-doctoral Fellowship European Research Council, 101041982 https://www.biorxiv.org/content/10.64898/2026.01.17.700056v1