Sodium Ions Regulate GPCR Activation by Remodeling Allosteric Coupling Networks and Hydration Patterns

Sodium ions (Na+) are key modulators of G-protein coupled receptor (GPCR) function, yet their mechanistic role remains incompletely understood. Here, we reveal a novel mode of Na+-mediated inactivation in the dopamine D2 receptor (DRD2), where Na+ reshapes long-range allosteric coupling networks and disrupts a continuous internal water column essential for activation. Using extensive molecular dynamics simulations and alchemical free energy calculations, we show that Na+ induces inactive-like residue interactions in the active state and triggers the formation of a distinct hydration gap. We also identify previously unreported Na+ binding sites and quantify their impact on the active-inactive state equilibrium by thermodynamic scanning. These findings provide mechanistic insights into Na+-driven allosteric regulation of GPCRs and highlight new opportunities for drug design targeting ion-sensitive receptor states. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=109 SRC="FIGDIR/small/714850v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@372084org.highwire.dtl.DTLVardef@137db0borg.highwire.dtl.DTLVardef@de210org.highwire.dtl.DTLVardef@174bdce_HPS_FORMAT_FIGEXP M_FIG C_FIG