Backbone variation in ensemble refinements of PDB entry 7k3t with different underlying disorder models. An equivalent figure with side chains is shown in Supplementary Fig. S12. Structures shown are as in Table 4. Rows are labelled with the disorder model used. Column 1: the input disorder for the ECHT disorder models. Column 2: the output ensemble in the area surrounding the active site (the catalytic His residue is indicated), including the p2 helix and the p5 loop. Column 3: the disorder in the p2 helix systematically decreases as more disorder is added to the underlying disorder model, but the ensembles are all qualitatively similar, confirming that the helix, although flexible, adopts only one distinct conformation. Column 4: the pTLS model suppresses disorder at the top of the p5 loop. Different ECHT disorder models systematically increase disorder in the B factors and correspondingly decrease disorder in the obtained ensemble. The ECHT level 1 ensemble is the most physically interpretable ensemble, since this contains all of the disorder in the ensemble apart from collective molecular motions. In the ECHT level 1+2 ensemble and the ECHT level 1+2+3 ensemble some of this disorder is now hidden in the B factors, and only the complex residue motions remain.