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FRET experiments can yield state-specific structural information on complex dynamic biomolecular assemblies. However, FRET experiments need to be combined with computer simulations to overcome their sparsity. We introduce (i) an automated FRET experiment design tool determining optimal FRET pairs for structural modeling, (ii) a protocol for efficient FRET-assisted computational structural modeling at multiple scales, and (iii) a quantitative quality estimate for judging the accuracy of determined structures. We tested against simulated and experimental data., Comment: 18 pages, 2 figures, 1 table

We used a hybrid fluorescence spectroscopic toolkit to monitor T4 Lysozyme (T4L) in action. By unraveling the kinetic and dynamic interplay of the conformational states, we sought to elucidate the dynamic structural biology of T4L. In particular, by combining single-molecule and ensemble multiparameter fluorescence detection, EPR spectroscopy, mutagenesis, and FRET-positioning and screening, we characterized three short-lived conformational states within the conformational landscape of the T4L over the ns-ms timescale. The use of 33 FRET-derived distance sets, to screen known T4L structures, revealed that T4L in solution mainly adopts the known open and closed states in exchange at 4 $\mu$s. A newly found minor state, undisclosed by at present more than 500 crystal structures of T4L and sampled at 230 $\mu$s, may be actively involved in the product release step in catalysis. The presented fluorescence spectroscopic toolkit is anticipated to accelerate the development of dynamic structural biology., Comment: 43 pages, 7 figures, Supporting Information 50 pages