Mutual Protein-Ligand Conformational Selection Drives cGMP vs. cAMP Selectivity in Protein Kinase G

Protein kinase G (PKG) is a major receptor of cGMP, and controls signaling pathways distinct from those regulated by cAMP. However, the contributions of the two substituents that differentiate cGMP from cAMP (i.e. 6-oxo and 2-NH2) to the cGMP- versus-cAMP selectivity of PKG remain unclear. Here, using NMR to map how binding affinity and dynamics of the protein and ligand vary along a ligand double-substitution cycle, we show that the contributions of the two substituents to binding affinity are surprisingly nonadditive. Such non-additivity stems primarily from mutual protein-ligand conformational selection, whereby not only does the ligand select for a preferred protein conformation upon binding, but also, the protein selects for a preferred ligand conformation. The 6-oxo substituent mainly controls the conformational equilibrium of the bound protein, while the 2-NH2 substituent primarily controls the conformational equilibrium of the unbound ligand (i.e. syn versus anti). Therefore, understanding the conformational dynamics of both the protein and ligand is essential to explain the cGMP-versus-cAMP selectivity of PKG. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study using NMR reveals that the contributions of the two substituents of cGMP to the binding affinity of PKG are surprisingly nonadditive, primarily due to mutual protein-ligand conformational selection. The 6-oxo substituent controls the conformational equilibrium of the bound protein, while the 2-NH2 substituent primarily controls the conformational equilibrium of the unbound ligand. Understanding the conformational dynamics of both the protein and ligand is essential to explain the cGMP-versus-cAMP selectivity of PKG.