Evolutionarily conserved phosphorylation and palmitoylation-dependent regulation of dopamine D1-like receptors in vertebrates

In the vertebrate central nervous system, dopamine is a neurotransmitter, acting as a modulator of variety of neuronal functions, including cognition, emotion, locomotor activity, hunger and satiety, and endocrine system regulation. Dopamine receptors are composed of D 1 , D 2 , D 3 , D 4 and D 5 receptors, which are classified into two major subtypes, D 1 -like (D 1 and D 5 ) and D 2 -like (D 2 , D 3 and D 4 ) dopamine receptors. D 1 -like receptors stimulate adenylyl cyclase  (AC) activity, whereas D 2 -like receptors inhibit AC activity and these receptors modulate many signaling pathways in dopaminergic synapses. Previous studies showed that post-translational protein phosphorylation and palmitoylation of mammalian D 1 receptors regulate functional properties, stability, cellular localization and membrane trafficking of the receptors. Here, I further focus on conservation of phosphorylation and palmitoylation sites found in vertebrate and invertebrate D 1 -like receptor homologs. Analysis of databases provides evidence to suggest that PKA- and GRKs-catalyzed phosphorylation sites of D 1 -like receptors have been completely conserved in the vertebrate lineage, in spite of the divergence of D 1 -like receptors full-length amino acid sequences during molecular evolution. These intracellular phosphorylated serine and threonine residues of D 1 -like receptors are evolutionarily conserved against mutation pressure throughout vertebrate species with a couple of exceptions. Furthermore, a PKC-mediated phosphorylation site of D 1 -like receptors is conserved in gnathostomes (jawed vertebrates) and not exist in agnathans (jawless vertebrates). Another phosphorylation site for PKC has been additionally acquired only in mammalian D 1 receptor orthologs. These findings suggest that the multiple kinases-dependent regulation of dopaminergic synapses by phosphorylation is so critical for complex vertebrate higher brain function.  Namely, dynamic regulation of dopaminergic synapses made possible by reversible phosphorylation of D1-like receptors may ensure the specific refined functions of vertebrate nervous systems. In contrast, broadly conserved palmitoylation sites in both vertebrate and invertebrate D 1 -like receptor homologs indicate that palmitoylated cysteines play crucial roles for sustaining the structural and functional regulations of D 1 -like receptors.