Force-Profile Analysis of the Cotranslational Folding of HemK and Filamin Domains: Comparison of Biochemical and Biophysical Folding Assays.

We have characterized the cotranslational folding of two small protein domains of different folds-the α-helical N-terminal domain of HemK and the β-rich FLN5 filamin domain-by measuring the force that the folding protein exerts on the nascent chain when located in different parts of the ribosome exit tunnel (force-profile analysis, or FPA), allowing us to compare FPA to three other techniques currently used to study cotranslational folding: real-time FRET, photoinduced electron transfer, and NMR. We find that FPA identifies the same cotranslational folding transitions as do the other methods, and that these techniques therefore reflect the same basic process of cotranslational folding in similar ways.