Protein distance and dynamics characteristics inferred from single-molecule FRET experiment

Comprising roughly one-third of all the proteins found in the human body, intrinsically disordered proteins (IDPs) play a vital role in numerous functions including signaling and transcription. These proteins lack defined structure, however, which limits the techniques available to characterize them.

One effective method for describing how IDPs fold and function is Förster resonance energy transfer (FRET). The efficiency of this energy transfer process between donor and acceptor chromophores indicates the distance over which the transfer occurs. However, accurately interpreting distances and dynamics from FRET data remains challenging. An international collaboration describes in The Journal of Chemical Physics a new, simpler technique they developed for inferring the end-end distance, along with the Flory exponent and radius of gyration, of a protein from a single FRET experiment.

The approach employs a distance distribution with a variable scaling factor called the Flory scaling exponent. This allows the distribution to be determined from the experiment rather than assumed at the outset, yet requires only the mean FRET efficiency or fluorescence lifetime information. The scaling exponent is allowed to vary with the solution conditions in which the protein is studied.

Implicit and explicit solvent simulations for 30 different protein sequences validated this approach. Yielding gyration radii within 10 percent of the true values, the team’s method was found not only to be more accurate than commonly used polymer models, but also to return a scaling exponent that agrees with those determined directly from molecular ensembles. By using an analytical distance distribution, computationally demanding molecular simulations are unnecessary.

The authors intend to investigate a similar approach for small-angle X-ray scattering, another method that provides structural information about IDPs.

Source: “Inferring properties of disordered chains from FRET transfer efficiencies,” by Wenwei Zheng, Gül H. Zerze, Alessandro Borgia, Jeetain Mittal, Benjamin Schuler, and Robert B. Best, The Journal of Chemical Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5006954 .