Fig. 3: HDX–MS profiles of MsmIMPDH showing a decrease in the dynamics of the CBS domain upon binding of ATP and GTP.

a Heat map of apo MsmIMPDH (constructed from 221 generated peptides) shows the deuteration levels of each amino acid residue in MsmIMPDH obtained at 4 °C over a time course of 2–120 s. Each line represents one time point (2 s, 5 s, 10 s, 20 s, and 2 min). The degree of deuteration is represented by the relative fractional uptake, scaled in rainbow colours from the minimum to the maximum observed uptake. The residues with no sequence coverage are shown as white gaps in the heat map. The sequence coverage is depicted by purple lines above the sequence. Differential heat maps of MsmIMPDH under conditions of (b) apo vs ATP, and (c) ATP–IMP vs ATP–GTP–IMP. Differences in the relative fractional uptake are displayed in a blue–white–red colour scale: residues with decreased accessibility are in blue, and residues with increased HDX are in red. d The ΔHDX changes of ATP–IMP vs ATP–GTP–IMP at 10 s are mapped on the MsmIMPDH monomer structure. Red indicates elevated deuteration, and blue less extensive deuteration of the given region. Hinge regions with residues involved in the binding of GTP (Arg108 and Lys222) are outlined by separate black frames. Deuterium uptake plots show the evolution in the deuteration of four representative peptides in the hinge region. In the graphs, each line represents one protein state, and each point represents one time point over a time course of 2–120 s. For comparison, the protein states are displayed by the same symbols. The drops observed in the HDX rate are displayed in light- and dark-blue colours.