Fig. 5
The active NrdEF structure is a flexible α2β2. a SEC–SAXS of a stoichiometric mixture of C382S holo-NrdE and NrdF under activating conditions (1 mM ATP, 250 µM TTP) revealed a predominant species (experimental profile shown in blue) with a molecular weight estimate39 of 246 kDa, consistent with an α2β2 species (actual MW of 243 kDa). Structural modeling was performed in AllosMod-FoXS40 using three different α2β2 starting models. Using a symmetric α2β2 docking model18 as a starting model underestimated the shoulder observed in the mid-q region (purple dash; χ2 = 20.43), suggesting that the solution structure is more open. In contrast, the expanded α2β2 starting model derived from the ASU of the NrdEF cryo-EM structure (Fig. 2e, right) overestimated the shoulder (orange dash; χ2 = 18.55), suggesting that the subunits are closer together in solution under activating conditions. An asymmetric α2β2 starting model based on an S. typhimurium structure (PDB: 2BQ1)33 yielded the best-fit conformer (black dash; χ2 = 2.25). SAXS profiles are shown in Kratky representation (q vs. Ixq2) to emphasize mid-q features. b Best-fit models of the asymmetric α2β2 (top) and symmetric α2β2 (bottom). Source data are provided as a Source Data file
