Preferential Coupling of Dopamine D2S and D2L Receptor Isoforms with Gi1 and Gi2 Proteins—In Silico Study

The dopamine D2 receptor belongs to rhodopsin-like G protein-coupled receptors (GPCRs) and it is an important molecular target for the treatment of many disorders, including schizophrenia and Parkinson’s disease. Here, computational methods were used to construct the full models of the dopamine D2 receptor short (D2S) and long (D2L) isoforms (differing with 29 amino acids insertion in the third intracellular loop, ICL3) and to study their coupling with Gi1 and Gi2 proteins. It was found that the D2L isoform preferentially couples with the Gi2 protein and D2S isoform with the Gi1 protein, which is in accordance with experimental data. Our findings give mechanistic insight into the interplay between isoforms of dopamine D2 receptors and Gi proteins subtypes, which is important to understand signaling by these receptors and their mediation by pharmaceuticals, in particular psychotic and antipsychotic agents.

Untangling ciliary access and enrichment of two rhodopsin-like receptors using quantitative fluorescence microscopy reveals cell-specific sorting pathways

Resolution limitations of optical systems are major obstacles for determining whether proteins are enriched within cell compartments. Here we use an approach to determine the degree of membrane protein ciliary enrichment that quantitatively accounts for the differences in sampling of the ciliary and apical membranes inherent to confocal microscopes. Theory shows that cilia will appear more than threefold brighter than the surrounding apical membrane when the densities of fluorescently labeled proteins are the same, thus providing a benchmark for ciliary enrichment. Using this benchmark, we examined the ciliary enrichment signals of two G protein–coupled receptors (GPCRs)—the somatostatin receptor 3 and rhodopsin. Remarkably, we found that the C-terminal VxPx motif, required for efficient enrichment of rhodopsin within rod photoreceptor sensory cilia, inhibited enrichment of the somatostatin receptor in primary cilia. Similarly, VxPx inhibited primary cilium enrichment of a chimera of rhodopsin and somatostatin receptor 3, where the dual Ax(S/A)xQ ciliary targeting motifs within the third intracellular loop of the somatostatin receptor replaced the third intracellular loop of rhodopsin. Rhodopsin was depleted from primary cilia but gained access, without being enriched, with the dual Ax(S/A)xQ motifs. Ciliary enrichment of these GPCRs thus operates via distinct mechanisms in different cells.

Down-regulation of PAR1 activity with a pHLIP-based allosteric antagonist induces cancer cell death

A pH(Low) Insertion Peptide (pHLIP)-based construct derived from the third intracellular loop (i3) of a G protein-coupled receptor (GPCR) induces a concentration- and pH-dependent cytotoxicity in cancer cells by down-regulating receptor activity. This strategy allows for a more selective intracellular delivery than current approaches.

Filamin A interaction with the CXCR4 third intracellular loop regulates endocytosis and signaling of WT and WHIM-like receptors

Key Points Filamin A interacts directly with the third intracellular loop and the C-terminal tail of CXCR4. Disruption of FLNA binding to the ICL3 attenuates signaling and restores CXCL12-mediated endocytosis of WHIM-like CXCR4 receptor mutants.