Funding Organization(s): Other private, National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS), National Institutes of Health/National Institute of Neurological Disorders and Stroke (NIH/NINDS)
Toxic dipeptide-repeat (DPR) proteins are produced from expanded G 4 C 2 repeats in the C9ORF72 gene, the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Two DPR proteins, poly-PR and poly-GR, repress cellular translation but the molecular mechanism remains unknown. Here we show that poly-PR and poly-GR of ≥20 repeats inhibit the ribosome's peptidyl-transferase activity at nanomolar concentrations, comparable to specific translation inhibitors. High-resolution cryogenic electron microscopy (cryo-EM) reveals that poly-PR and poly-GR block the polypeptide tunnel of the ribosome, extending into the peptidyl-transferase center (PTC). Consistent with these findings, the macrolide erythromycin, which binds in the tunnel, competes with poly-PR and restores peptidyl-transferase activity. Our results demonstrate that strong and specific binding of poly-PR and poly-GR in the ribosomal tunnel blocks translation, revealing the structural basis of their toxicity in C9ORF72-ALS/FTD.
Department of Neurology, UMass Chan Medical School, 368 Plantation Street, Worcester, MA, 01605, USA. Fen-Biao.Gao@umassmed.edu.