Differential G protein activation by the long and short isoforms of the dopamine D 2 receptor

The dopamine D receptor is expressed as a short (D2S) and a long (D2L) isoform with 29 additional amino acids in the third intracellular loop. The D2S isoform shows higher presynaptic expression than the D2L isoform, and decreased D2S expression has recently been linked to an increased risk for schizophrenia. Here, we present the first investigation, at receptor isoform level, of kinetic differences in the G protein activation profiles of the D2S, compared with the D2L isoform. We employed a NanoBRET-based approach to G protein dissociation to interrogate the time-resolved coupling profile of 3×HA-tagged D2L and D2S to Gα proteins in vitro. Using dopamine as a D receptor agonist, we observed a more pronounced activation of Gα and Gα than Gα proteins by D2L compared with D2S. This differentiation was not observed for D2S, which activated Gα and Gα with lower efficacy than D2L. These signalling differences were preserved on second messenger level and were not due to differences in receptor expression. Expanding to a set of seven full and partial D receptor agonists showed these effects were not restricted to dopamine but rather a mutual, receptor-associated property. Contrasting this trend, we found that D2S activated G proteins faster than D2L upon full receptor activation. The findings highlight that both D2L and D2S are mechanistically able to activate all non-visual Gα proteins. Thereby, they add to previous reports about isoform-specificity to certain Gα proteins observed in specific cell types.