Figure 6. Dynamic characteristics of GMPR complexes revealed by high resolution ³¹P field cycling NMR relaxometry.

(A) Multiple binding modes for substrate and cofactors. Two distinct binding modes are observed for IMP and GMP in their catalytically active NADP⁺ complexes. The cofactor also has two distinct binding modes in these complexes as shown by the effects of D₂O on relaxation, albeit with similar ³¹P-proton relaxer distances. These binding modes are indicated by the positions of the two ellipses. When the binding mode cannot be distinguished by the values of τ/R₀, the ellipse is positioned in the center. A third conformation, indicated by the dashed ellipse, is observed in the dIMP-cofactor complex. The extrapolated ³¹P-proton relaxer distances are show in Å. (B) Distinct dynamic states are observed in wild-type enzyme and D219A and with ribose and deoxyribose substrates as evidenced by values of τ.