Flexibility characterization of DENV-4 NS2B18NS3, showing an ensemble of five possible positions for the protease domain based on EOM 2.0 analysis. (a) Different views of the ensemble models in cartoon representation with the helicase domain of DENV-4 NS2B18NS3 in orange and the flexible protease domain in blue, together with their conformational contributions (purple, 25%; light blue, 25%; purple blue, 25%; blue, 13%; slate blue, 13%; the connecting linkers are rendered semi-transparent and NS2B18 is in green). (b) Comparison between the R
g distributions (pool, black; ensemble, red) shows a random flexibility as confirmed by R
flex (∼81% versus ∼87%, with 87% as the threshold value for randomness) and R
σ = 0.90. The R
g corresponding to the DENV-4 NS2B18NS3 crystal structure (PDB entry 2vbc) is labelled on the curve (light blue arrow). (c) Small-angle X-ray scattering pattern (black circles) and calculated ensemble scattering profiles (red line) with a discrepancy χ2 of 0.237.