Transmembrane five effects on functional selectivity at the dopamine D2L receptor

Abstract

Mechanisms of functional selectivity (ligand-induced differential signaling) at the dopamine D2 receptor were studied by addressing how binding interactions at specific amino acids affect ligand function. Molecular modeling was used to dock the structurally similar compounds dinapsoline (DNS) and dinoxyline (DNX) into the active site of the hD2L receptor, after which point mutants of the receptor were made to test each hypothesis. Binding studies conducted with DNS support H bonding of the p-OH with both serine 5.46(197) and threonine 3.37(119) whereas the m-OH interacts with serine 5.42(193). Conversely, data with DNX supports H-bonding of the p-OH with only T3.37 whereas the m-OH interacts with both serine 5.42 and 5.46. Additionally, an ether internal to DNX also forms H-bonds with serine 5.42. Subsequent functional analyses of site-directed mutant receptors support the hypothesis that specific ligand-residue interactions can affect the observed functional differences in cAMP inhibition, MAPK phosphorylation, and AA-release. Developing a structure-based understanding of functional selectivity is heuristically useful for understanding the mechanisms of GPCR activation, and also may suggest the design of novel small molecules with unique mixtures of functional properties.