Figure 6. Identification of the site on PDI that interacts with partly-folded BPTI.

¹H-¹⁵N HSQC spectra of 0.25 mM ¹⁵N-labeled bb'x fragment of PDI recorded at 25°C, A) in absence of any ligand, and B) in presence of 50 µM partly-folded BPTI. Peaks for the indole NH resonance of Trp 347 are highlighted within a dashed box. Chemical shift perturbations were measured from peaks in the spectrum in absence of ligand to the nearest peak found in the spectrum recorded in presence of ligand, and the net chemical shift perturbation was calculated as Δ¹⁵N/6+Δ¹H. Net chemical shift perturbations were plotted versus sequence position in PDI, C) for data in presence of 50 µM ligand (panel B above) and D) for data in presence of 0.25 mM ligand (spectrum not shown). Blue bars represent shifts of peaks identified in the target spectrum, maroon bars represent shifts from peaks that could not be identified in the target spectrum, presumed to be due to line broadening. The cartoon below each graph indicates the position of each domain in the bb'x construct. The chemical shift perturbations seen in the presence of 0.25 mM ligand (panel D) are shown mapped onto the structure (PDB 2K18) in E), where red indicates perturbations >0.1 ppm and yellow indicates perturbations >0.06 ppm.