Cotranslational Protein Folding inside the Ribosome Exit Tunnel

• Cotranslational folding is studied by arrest-peptide-mediated force measurements
• Single-molecule measurements show that a pulling force prevents ribosome stalling
• A ribosome-tethered zinc-finger domain is visualized by cryo-EM (electron microscopy)
• The zinc-finger domain is shown to fold deep inside the ribosome exit tunnel

SummaryAt what point during translation do proteins fold? It is well established that proteins can fold cotranslationally outside the ribosome exit tunnel, whereas studies of folding inside the exit tunnel have so far detected only the formation of helical secondary structure and collapsed or partially structured folding intermediates. Here, using a combination of cotranslational nascent chain force measurements, inter-subunit fluorescence resonance energy transfer studies on single translating ribosomes, molecular dynamics simulations, and cryoelectron microscopy, we show that a small zinc-finger domain protein can fold deep inside the vestibule of the ribosome exit tunnel. Thus, for small protein domains, the ribosome itself can provide the kind of sheltered folding environment that chaperones provide for larger proteins.

Graphical AbstractFigure optionsDownload as PowerPoint slide