Figure 3. Initial foldons in PpiB and PpiA using t_50% from local HDX‐MS analysis.

• A, B
  Folding kinetics of PpiB (A) and PpiA (B) at 25 or 4°C, monitored by local HDX‐MS (Dataset EV4; n = 3 biological repeats), were analysed by PyHDX to determine the folded fractions per residue (Dataset EV5); see pipeline of analysis in Fig EV3B and folding times in Fig EV3E. For each peptide, 100% folding was set to the D‐uptake of the native protein peptide and 0% folding to the D‐uptake of the same peptide under fully deuterated conditions. Initial foldons were assigned by plotting the time needed to reach 50% of folded fraction (t_50%; y‐axis; Dataset EV5) along the linear sequence (x‐axis), at both temperatures (as indicated). Only up to 1 min data are shown here (see extended dataset colour map in Appendix Fig S2; raw data in Dataset EV4). The alignment index is based on the sequence of PpiA (extended N‐tail; missing loop between β6‐β7; Appendix Fig S1D). Gaps: residues absent in one of the twins, prolines or no experimental coverage. Colour boxes below the linear secondary structure map (top) indicate foldons, named in alphabetical order. Grey bar: unstructured fast folding regions (Fig EV3D) omitted from analysis.
• C, D
  Foldons, colour‐coded as in the left panels, are indicated relative to their time of formation on the PpiB (1LOP; C) and PpiA (1V9T; D) 3D structures.The indicated time points were as follows: for PpiB, 25°C (t _80% of 0.29‐0.33‐0.42‐0.47 min); for PpiB, 4°C (t _80% of 0.09‐0.29‐0.90‐1.75 min); for PpiA, 25°C (t _80% of 0.24‐0.33‐0.47‐0.51 min); for PpiA, 4°C (t _50% of 0.34‐0.55‐0.79‐0.99 min; Fig EV3E, Dataset EV5).