Diffusion Flashing into View

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Science  02 Mar 2007:
Vol. 315, Issue 5816, pp. 1194
DOI: 10.1126/science.315.5816.1194b

Kinetic measurements with microsecond resolution have offered substantial insight into the folding mechanisms of proteins. However, before the folding event, protein chains undergo diffusional motion on a time scale of tens of nanoseconds that has proven challenging to probe. This time window is of particular interest because of its ready accessibility to theory. Nettels et al. have used single-molecule spectroscopy to resolve the nanosecond dynamics of unfolded cold-shock protein from Thermotoga maritima. They labeled the protein's ends with fluorophores and then detected changes in the chain geometries through shifts in the emitted photon statistics due to Förster resonance energy transfer. By comparing the resulting autocorrelation functions with model calculations, they could extract diffusion coefficients and reconfiguration times, which in turn contribute to a quantitative picture of the free-energy landscape. A significant (fivefold) decrease in the diffusion coefficient was observed on chain collapse, a pre-folded state induced by lowering the concentration of denaturant. — JSY

Proc. Natl. Acad. Sci. U.S.A. 104, 2655 (2007).

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