The human ribosome modulates multidomain protein biogenesis by delaying cotranslational domain docking.

Proteins with multiple domains are intrinsically prone to misfold, yet fold efficiently during their synthesis on the ribosome. This is especially important in eukaryotes, where multidomain proteins predominate. Here we sought to understand how multidomain protein folding is modulated by the eukaryotic ribosome. We used hydrogen-deuterium exchange mass spectrometry and cryo-electron microscopy to characterize the structure and dynamics of partially synthesized intermediates of a model multidomain protein. We find that nascent subdomains fold progressively during synthesis on the human ribosome, templated by interactions across domain interfaces. The conformational ensemble of the nascent chain is tuned by its unstructured C-terminal segments, which keep interfaces between folded domains in dynamic equilibrium until translation termination. This contrasts with the bacterial ribosome, on which domain interfaces form early and remain stable during synthesis. Delayed domain docking may avoid interdomain misfolding to promote the maturation of multidomain proteins in eukaryotes.