Protein Conformational Dynamics Probed by Single-Molecule Electron Transfer

TLDR

Electron transfer probes angstrom‑scale structural changes in single proteins, exemplified by flavin reductase where flavin fluorescence is quenched by a nearby tyrosine via photo‑induced electron transfer. Fluorescence lifetimes of single flavin molecules were measured photon‑by‑photon to track time‑dependent flavin‑tyrosine distance variations. Analysis yielded the potential of mean force between flavin and tyrosine and revealed conformational fluctuations across microsecond‑to‑second timescales, indicating multiple interconverting conformers that may underlie catalytic variability.

Abstract

Electron transfer is used as a probe for angstrom-scale structural changes in single protein molecules. In a flavin reductase, the fluorescence of flavin is quenched by a nearby tyrosine residue by means of photo-induced electron transfer. By probing the fluorescence lifetime of the single flavin on a photon-by-photon basis, we were able to observe the variation of flavin-tyrosine distance over time. We could then determine the potential of mean force between the flavin and the tyrosine, and a correlation analysis revealed conformational fluctuation at multiple time scales spanning from hundreds of microseconds to seconds. This phenomenon suggests the existence of multiple interconverting conformers related to the fluctuating catalytic reactivity.