Protein synthesis in the developing neocortex at near-atomic resolution reveals Ebp1-mediated neuronal proteostasis at the 60S tunnel exit

Proteostasis must be finely tuned in the nervous system, as it represents an essential feature of neurodevelopment, and dominant pathology in neurodegenerative disease. At the gateway of proteostasis is the ribosome; however, the architecture of ribosomal complexes in the developing mammalian brain has not been visualized. In this study, we analyze the molecular architecture of ex vivo embryonic and perinatal mouse neocortical ribosomes, revealing Ebp1 as a 60S peptide tunnel exit binding factor at near-atomic resolution by multiparticle cryo-electron microscopy. The impact of Ebp1 on the neuronal proteome was analyzed by pSILAC and BONCAT coupled mass spectrometry, implicating Ebp1 in neurite outgrowth proteostasis, with in vivo embryonic Ebp1 knockdown resulting in neurite outgrowth dysregulation. This study constitutes the first near-atomic resolution structure of actively translating ribosomes ex vivo from the nervous system, and visualizes Ebp1 as a chaperone of protein synthesis at the 60S peptide tunnel exit in neocortical neurogenesis.