Figure 6

Quantifying the PPIA interaction with heparin at atomic resolution. A) ¹⁵N-HSQC spectra of 0.5 mM ¹⁵N-PPIA alone (black) and in complex with 3 mM heparin (red). B) Residues that exhibit chemical shifts greater than 0.1 ppm upon engaging heparin in either ¹⁵N or ¹H dimensions are highlighted (red) and are all located within the PPIA active site. C) Based on the measured ¹⁵N-PPIA chemical shift changes upon titration with heparin, the binding isotherms were used to estimate a K_D of 2.5 ± 0.3 mM. Shown are the binding isotherms for the ¹⁵N chemical shift changes of K82 and T152. All experiments were conducted at 600 MHz at 25°C.