Detection of Concordance between Transcriptional Levels of GPCRs and Receptor-Activity-Modifying Proteins

Summary: A recent phylogenetic analysis showed global co-evolution of G protein-coupled receptors (GPCRs) and receptor-activity-modifying proteins (RAMPs) suggesting global interactions between these two protein families. Experimental validation of these findings is challenging because in humans whereas there are only three genes encoding RAMPs, there are about 800 genes encoding GPCRs. Here, we report an experimental approach to evaluate GPCR-RAMP interactions. As a proof-of-concept experiment, we over-expressed RAMP2 in HEK293T cells and evaluated the effect on the transcriptional levels of 14 representative GPCRs that were selected based on the earlier phylogenetic analysis. We utilized a multiplexed error-correcting fluorescence in situ hybridization (MERFISH) method to detect message levels for individual GPCRs in single cells. The MERFISH results showed changes in GPCR message levels with RAMP2 over-expression in a concordant pattern that was predicted by the earlier phylogenetic analysis. These results provide additional evidence that GPCR-RAMP interactions are more widespread than previously appreciated and that these interactions have functional consequences. : Biological Sciences; Cell Biology; Molecular Biology Subject Areas: Biological Sciences, Cell Biology, Molecular Biolog

Bioorthogonal fluorescent labeling of functional G-protein-coupled receptors

Novel methods are required for site-specific, quantitative fluorescence labeling of G protein-coupled receptors (GPCRs) and other difficult-to-express membrane proteins. Ideally, fluorescent probes should perturb native structure and function as little as possible. We evaluated bioorthogonal reactions to label genetically encoded p-acetyl-l-phenylalanine (AcF) or p-azido-l-phenylalanine (azF) residues in receptors heterologously expressed in mammalian cells. We found that keto-selective reagents were not truly bioorthogonal, possibly due to posttranslational protein oxidation reactions. In contrast, the strain-promoted [3+2] azide–alkyne cycloaddition (SpAAC) with dibenzocyclooctyne (DIBO) reagents yielded stoichiometric conjugates with azF-rhodopsin while undergoing negligible background reactions. As one useful application, we used Alexa488-rhodopsin to measure the kinetics of ligand uptake and release in membrane-mimetic bicelles using a novel fluorescence-quenching assay

Spectral tuning of ultraviolet cone pigments: An interhelical lock mechanism

Ultraviolet (UV) cone pigments can provide insights into the molecular evolution of vertebrate vision since they are nearer to ancestral pigments than the dim-light rod photoreceptor rhodopsin. While visible-absorbing pigments contain an 11-cis retinyl chromophore with a protonated Schiff-base (PSB11), UV pigments uniquely contain an unprotonated Schiff-base (USB11). Upon F86Y mutation in model UV pigments, both the USB11 and PSB11 forms of the chromophore are found to coexist at physiological pH. The origin of this intriguing equilibrium remains to be understood at the molecular level. Here, we address this phenomenon and the role of the USB11 environment in spectral tuning by combining mutagenesis studies with spectroscopic (UV-vis) and theoretical [DFT-QM/MM (SORCI+Q//B3LYP/6-31G(d): Amber96)] analysis. We compare structural models of the wild-type (WT), F86Y, S90A and S90C mutants of Siberian hamster ultraviolet (SHUV) cone pigment to explore structural rearrangements that stabilize USB11 over PSB11. We find that the PSB11 forms upon F86Y mutation and is stabilized by an "inter-helical lock" (IHL) established by hydrogen-bonding networks between transmembrane (TM) helices TM6, TM2, and TM3 (including water w2c and amino acid residues Y265, F86Y, G117, S118, A114, and E113). The findings implicate the involvement of the IHL in constraining the displacement of TM6, an essential component of the activation of rhodopsin, in the spectral tuning of UV pigments. \ua9 2013 American Chemical Society

High-affinity binding of chemokine analogs that display ligand bias at the HIV-1 coreceptor CCR5

The chemokine receptor CCR5 is a drug target to prevent transmission of HIV/AIDS. We studied four analogs of the native chemokine regulated, on activation, normal T-cell-expressed, and secreted (RANTES) (CCL5) that have anti-HIV potencies of around 25 pM, which is more than four orders of magnitude higher than that of RANTES itself. It has been hypothesized that the ultrahigh potency of the analogs is due to their ability to bind populations of receptors not accessible to native chemokines. To test this hypothesis, we developed a homogeneous dual-color fluorescence cross-correlation spectroscopy assay for saturation- and competition-binding experiments. The fluorescence cross-correlation spectroscopy assay has the advantage that it does not rely on competition with radioactively labeled native chemokines used in conventional assays. We prepared site-specifically labeled fluorescent analogs using native chemical ligation of synthetic peptides, followed by bioorthogonal fluorescent labeling. We engineered a mammalian cell expression construct to provide fluorescently labeled CCR5, which was purified using a tandem immunoaffinity and size-exclusion chromatography approach to obtain monomeric fluorescent CCR5 in detergent solution. We found subnanomolar binding affinities for the two analogs 5P12-RANTES and 5P14-RANTES and about 20-fold reduced affinities for PSC-RANTES and 6P4-RANTES. Using homologous and heterologous competition experiments with unlabeled chemokine analogs, we conclude that the analogs all bind at the same binding site, whereas the native chemokines (RANTES and MIP-1α) fail to displace bound fluorescent analogs even at tens of micromolar concentrations. Our results can be rationalized with de novo structural models of the N-terminal tails of the synthetic chemokines that adopt a different binding mode as compared to the parent compound

An oxytocin/vasopressin-related neuropeptide modulates social foraging behavior in the clonal raider ant

Oxytocin/vasopressin-related neuropeptides are highly conserved and play major roles in regulating social behavior across vertebrates. However, whether their insect orthologue, inotocin, regulates the behavior of social groups remains unknown. Here, we show that in the clonal raider ant Ooceraea biroi, individuals that perform tasks outside the nest have higher levels of inotocin in their brains than individuals of the same age that remain inside the nest. We also show that older ants, which spend more time outside the nest, have higher inotocin levels than younger ants. Inotocin thus correlates with the propensity to perform tasks outside the nest. Additionally, increasing inotocin pharmacologically increases the tendency of ants to leave the nest. However, this effect is contingent on age and social context. Pharmacologically treated older ants have a higher propensity to leave the nest only in the presence of larvae, whereas younger ants seem to do so only in the presence of pupae. Our results suggest that inotocin signaling plays an important role in modulating behaviors that correlate with age, such as social foraging, possibly by modulating behavioral response thresholds to specific social cues. Inotocin signaling thereby likely contributes to behavioral individuality and division of labor in ant societies.ISSN:1544-9173ISSN:1545-788