NMR snapshots of nascent chains emerging from the ribosome during biosynthesis

NMR spectroscopy is a powerful tool to study the dynamic process of how proteins acquire their biological fold at near-atomic resolution. Advances in spectroscopic and biochemical approaches have now expanded the ability of NMR methods to probe increasingly larger biological machinery including the 2.4-MDa 70S E. coli ribosome, where polypeptide chains are assembled. Detailed structures of the ribosome have been determined by X-ray crystallography and cryo-electron microscopy studies that describe the rigid ribosomal core and exit tunnel that the nascent chain must pass during its biosynthesis. However, most folding occurs when the nascent chain has emerged beyond the exit tunnel and it is here where NMR spectroscopy is uniquely able to provide high-resolution structural insights into on its co-translational folding. In this review, we will discuss recent progress in NMR studies of ribosome-bound nascent chain complexes, highlighting the emerging role of the ribosome and how these results are shaping our understanding of co-translational protein folding in the cell.