Role of the fourth intracellular loop of D1-like dopaminergic receptors in conferring subtype-specific signaling properties

Abstract 

We investigate whether the fourth intracellular loop (IL4) of D1 and D5 dopaminergic receptors (D1R, D5R) confers D1-like subtype-specific signaling properties. Using chimeric receptors (D1R-IL4B and D5R-IL4A), we show that swapping of IL4 leads to a switch in dopamine affinity and constitutive activity of D1R and D5R. Dopamine potency was reduced for both chimeras in comparison with wild-type receptors. Moreover, dopamine-mediated maximal activation was drastically increased in cells expressing D1R-IL4B when compared with those harboring D5R-IL4A or wild-type receptors. In conclusion, IL4 plays a pivotal role in imparting subtype-specific ligand binding and activation properties to highly homologous seven-transmembrane receptors.

Keywords:  Dopamine, Seven-transmembrane receptor, Helix-8, Ligand binding, Constitutive activation, G protein

Abbreviations:  AC, adenylyl cyclase, AR, adrenergic receptor, B_max, maximal binding capacity, CT, cytoplasmic tail, DA, dopamine, GPCR, G protein-coupled receptor, H8, α-helix 8 region, HEK293, human embryonic kidney 293, IL4, fourth intracellular loop, MEM, minimal essential medium, PBS, phosphate-buffered saline, PCR, polymerase chain reaction, TM7, transmembrane region 7