Analysis of protein-protein interactions using bioluminescence resonance energy transfer

Monitoring Opioid Receptor Interaction in Living Cells by Bioluminescence Resonance Energy Transfer (BRET)

Bioluminescence resonance energy transfer (BRET ) is a natural phenomenon that has been successfully applied for the study of protein-protein interactions, including opioid receptor oligomers. The discovery of opioid receptor homomers and heteromers has brought to the discovery of new functions and new way of signaling and trafficking; therefore, opioid receptor oligomers may be considered as novel drug targets. Fusing receptors of interest with Renilla luciferase and with a fluorescent protein (such as EYFP ) it is possible to study opioid receptor dimerization using BRET .

Monitoring opioid receptor dimerization in living cells by bioluminescence resonance energy transfer (BRET)

Bioluminescence resonance energy transfer (BRET) is a natural phenomenon that has been successfully applied for the study of protein-protein interactions, including opioid receptor oligomers. The discovery of opioid receptor homomers and heteromers has brought to the finding of new functions and new way of signaling and trafficking; therefore, opioid receptor oligomers may be considered as novel drug targets. Fusing receptors of interest with Renilla luciferase and with a fluorescent protein (such as EYFP), it is possible to study opioid receptor dimerization using BRET.

Biophysical Detection of Diversity and Bias in GPCR Function

Guanine nucleotide binding protein (G protein)-coupled receptors (GPCRs) function in complexes with a range of molecules and proteins including ligands, G proteins, arrestins, ubiquitin, and other receptors. Elements of these complexes may interact constitutively or dynamically, dependent upon factors such as ligand binding, phosphorylation, and dephosphorylation. They may also be allosterically modulated by other proteins in a manner that changes temporally and spatially within the cell. Elucidating how these complexes function has been greatly enhanced by biophysical technologies that are able to monitor proximity and/or binding, often in real time and in live cells. These include resonance energy transfer approaches such as bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET). Furthermore, the use of fluorescent ligands has enabled novel insights into allosteric interactions between GPCRs. Consequently, biophysical approaches are helping to unlock the amazing diversity and bias in G protein-coupled receptor signaling.

Heterodimerization of human apelin and kappa opioid receptors: roles in signal transduction

Apelin receptor (APJ) and kappa opioid receptor (KOR) are members of the family A of G protein-coupled receptors (GPCRs). These two receptors are involved in the central nervous system regulation of the cardiovascular system. Here, we explore the possibility of heterodimerization between APJ and KOR and investigate their novel signal transduction characteristics. Co-immunoprecipitation (Co-IP), co-localization and bioluminescence resonance energy transfer (BRET) assays confirmed the heterodimerization of APJ and KOR. In APJ and KOR stably transfected HEK293 cells, treatment with APJ ligand apelin-13 or KOR ligand dynorphinA (1-13) resulted in higher phosphorylation levels of extracellular-regulated kinases 1/2 (ERK1/2) compared to HEK293 cells transfected with either APJ or KOR alone. The siRNA knockdown of either APJ or KOR receptor in human umbilical vein endothelial cells (HUVECs) resulted in significant reduction of the apelin-13 induced ERK activation. Additionally both forskolin (FSK)-induced cAMP levels and cAMP response element reporter activities were significantly reduced, whereas the serum response element luciferase (SRE-luc) reporter activity was significantly upregulated. Moreover, the ERK phosphorylation and SRE-luc activity were abrogated by the protein kinase C (PKC) inhibitor. These results demonstrate for the first time that human APJ forms a heterodimer with KOR and leads to increased PKC and decreased protein kinase A activity leading to a significant increase in cell proliferation, which may translate to the regulation of diverse biological actions and offers the potential for the development of more selective and tissue specific drug therapies.

Next generation functional proteomics in non-model plants: A survey on techniques and applications for the analysis of protein complexes and post-translational modifications

The congruent development of computational technology, bioinformatics and analytical instrumentation makes proteomics ready for the next leap. Present-day state of the art proteomics grew from a descriptive method towards a full stake holder in systems biology. High throughput and genome wide studies are now made at the functional level. These include quantitative aspects, functional aspects with respect to protein interactions as well as post translational modifications and advanced computational methods that aid in predicting protein function and mapping these functionalities across the species border. In this review an overview is given of the current status of these aspects in plant studies with special attention to non-genomic model plants.

Allostery at G protein-coupled receptor homo- and heteromers: uncharted pharmacological landscapes

For many years seven transmembrane domain G protein-coupled receptors (GPCRs) were thought to exist and function exclusively as monomeric units. However, evidence both from native cells and heterologous expression systems has demonstrated that GPCRs can both traffic and signal within higher-order complexes. As for other protein-protein interactions, conformational changes in one polypeptide, including those resulting from binding of pharmacological ligands, have the capacity to alter the conformation and therefore the response of the interacting protein(s), a process known as allosterism. For GPCRs, allosterism across homo- or heteromers, whether dimers or higher-order oligomers, represents an additional topographical landscape that must now be considered pharmacologically. Such effects may offer the opportunity for novel therapeutic approaches. Allosterism at GPCR heteromers is particularly exciting in that it offers additional scope to provide receptor subtype selectivity and tissue specificity as well as fine-tuning of receptor signal strength. Herein, we introduce the concept of allosterism at both GPCR homomers and heteromers and discuss the various questions that must be addressed before significant advances can be made in drug discovery at these GPCR complexes.

Imaging-based approaches to understanding g protein-coupled receptor signalling complexes

In the last 10 years, imaging assays based on resonance energy transfer (RET) and protein fragment complementation have made it possible to study interactions between components of G protein-coupled receptor (GPCR) signalling complexes in living cells under physiological conditions. Here, we consider the history of such approaches, the current tools available and how they have changed our understanding of GPCR signalling. We also discuss some theoretical and methodological issues important when combining the different types of assay.

Real-time BRET assays to measure G protein/effector interactions

Advances in imaging assays based on resonance energy transfer (RET) have made it possible to study protein/protein interactions in living cells under physiological conditions. It is now possible to measure the kinetics of changes in these interactions in response to ligand stimulation in real time. Here we describe protocols for these assays focusing on the basal and ligand-stimulated interaction between tagged Gβγ subunits and adenylyl cyclase II. We describe relevant positive and negative controls and various experimental considerations for optimization of these experiments.