Extended Data Fig. 10: SAXS analysis shows significant compaction of the didomain aCC2 construct upon addition of substrates.

a, EFA-separated SAXS profiles of aCC2 (black) and aCC2 incubated with 1 mM ATP/L-Phe (blue), shown as a semilog plot, display a clear change in shape upon the addition of 1 mM ATP/L-Phe, indicative of a change in protein conformation. The intensity was normalized by I(0) for comparison. b, Plotting the scattering profiles in Kratky representation emphasizes the change in the mid-q region (~0.1–0.2 Å⁻¹), which is sensitive to ___domain arrangements. The addition of substrates leads to a tightening in the shape of the Kratky peak, consistent with a significant compaction. c, d, Comparison of EOM fits done by defining 2 rigid bodies (A-___domain, residues 17–527, and PCP, 537–614) to EOM fits done by defining 3 rigid bodies (A^N subdomain, 17–427, A^C subdomain, 432–527, and PCP, 537–614). (c), Fits to the aCC2 scattering in the absence of substrate. The two fits overlay well; the quality of the 2-rigid body fit (solid curve, χ² = 1.98) is comparable to the 3-rigid body fit (dashed curve, χ² = 1.71). (d), Fits to the aCC2 with 1 mM ATP/L-Phe scattering. The two fits again overlay well; the quality of the 2-rigid body fit (solid curve, χ² = 2.81) is comparable to the 3-rigid body fit (dashed curve, χ² = 2.63). As adding an additional degree of freedom in the 3-rigid bodies analysis does not significantly improve the quality of the fits from the 2-rigid bodies analysis, our SEC-SAXS data provide independent experimental support to our smFRET-guided MD modelling (Extended Data Fig. 1).

Source data