<p>(A) Downfield region of HSQC spectra of <sup>15</sup>N-labeled P-domain (residues 211–261) titrated with increasing amounts of the non-catalytic domain of PDIR. The spectra show specific chemical shift changes for residues Ile225 and Ile249. (B) Plot of weighted-average <sup>1</sup>H and <sup>15</sup>N chemical shift changes in the <sup>15</sup>N-labeled calreticulin P-domain upon addition of the unlabeled PDIR domain. (C) Mapping of the chemical shifts measured onto the NMR structure of the calreticulin P-domain (PDB code 1k9c). Magenta indicates a large chemical shift change (>0.1 ppm); white indicates no change detected. Residues showing chemical shift changes above 0.07 ppm are labeled. (D) Surface charge representation of the P-domain. Negative charge is shown in red, positive charge is in blue. (E) Titration of the <sup>15</sup>N-labeled P-domain with the PDIR non-catalytic domain in the presence of 0.5 M ammonium sulfate. The overlay corresponds to the P-domain/PDIR molar ratio of 1∶0 (red), 1∶1 (yellow) and 1∶2 (blue). (F) Titration of the <sup>15</sup>N-labeled PDIR non-catalytic domain with increasing amounts of unlabeled P-domain results in shifts and disappearance of a number of peaks. Overlay shows spectra at the PDIR/P-domain molar ratio of 1∶0 (red), 1∶1 (yellow), 1∶2 (cyan), 1∶4 (purple) and 1∶8 (blue).</p
