Rasmus Jorgensen

Novo Nordisk, København, Capital Region, Denmark

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Publications (13)42.26 Total impact

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    ABSTRACT: It has been hypothesized that amphipathic peptides might bind to membranes prior to activating their cognate receptors, but this has proven difficult to test. The peptide hormone PYY3-36 is believed to perform its appetite-suppressing actions through binding to hypothalamic Y2 receptors. It has been proposed that PYY3-36 via its amphipathic α-helix binds to the plasma membrane prior to receptor docking. Here, our aim was to study the implication of this hypothesis using new analogs of PYY3-36. We first studied membrane binding of PYY3-36. Next, we designed a series of PYY3-36 analogs to increase membrane-binding affinity by substituting the N-terminal segment with a de novo designed α-helical, amphipathic sequence. These 2-helix variants of PYY3-36 were assembled by solid-phase peptide synthesis. Pharmacological studies demonstrated that even though the native peptide sequence was radically changed, highly active Y2 receptor agonists were generated. A potent analog, with a Kd of 4 nM for membranes, was structurally characterized by NMR in the membrane-bound state, which clearly showed that it formed the expected 2-helix. The topology of the peptide-micelle association was studied by paramagnetic relaxation enhancement using a spin label, which confirmed that the hydrophobic residues bound to the membrane. Our studies further support the hypothesis that PYY3-36 associates with the membrane and indicate that this can be used in the design of novel molecules with high receptor binding potency. These observations are likely to be generally important for peptide hormones and biopharmaceutical drugs derived from them. This new 2-helix variant of PYY3-36 will be useful as a tool compound for studying peptide-membrane interactions.
    Journal of Peptide Science 08/2012; 18(9):579-87. · 2.07 Impact Factor
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    ABSTRACT: The insulin receptor (IR) belongs to the receptor tyrosine kinase super family and plays an important role in glucose homeostasis. The receptor interacts with several large docking proteins that mediate signaling from the receptor, including the insulin receptor substrate (IRS) family and Src homology-2-containing proteins (Src). Here, we applied the bioluminescence resonance energy transfer 2 (BRET2) technique to study the IR signaling pathways. The interaction between the IR and the substrates IRS1, IRS4 and Shc was examined in response to ligands with different signaling properties. The association between IR and the interacting partners could successfully be monitored when co-expressing green fluorescent protein 2 (GFP2) tagged substrates with Renilla reniformis luciferase 8 (Rluc8) tagged IR. Through additional optimization steps, we developed a stable and flexible BRET2 assay for monitoring the interactions between the IR and its substrates. Furthermore, the insulin analogue X10 was characterized in the BRET2 assay and was found to be 10 times more potent with respect to IRS1, IRS4 and Shc recruitment compared to human insulin. This study demonstrates that the BRET2 technique can be applied to study IR signaling pathways, and that this assay can be used as a platform for screening and characterization of IR ligands.
    Journal of Receptor and Signal Transduction Research 01/2012; 32(2):57-64. · 1.63 Impact Factor
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    ABSTRACT: The superfamily of the seven transmembrane G-protein-coupled receptors (7TM/GPCRs) is the largest family of membrane-associated receptors. GPCRs are involved in the pathophysiology of numerous human diseases, and they constitute an estimated 30-40% of all drug targets. During the last two decades, GPCR oligomerization has been extensively studied using methods like bioluminescence resonance energy transfer (BRET) and today, receptor-receptor interactions within the GPCR superfamily is a well-established phenomenon. Evidence of the impact of GPCR oligomerization on, e.g., ligand binding, receptor expression, and signal transduction indicates the physiological and pharmacological importance of these receptor interactions. In contrast to the larger and more thoroughly studied GPCR subfamilies A and C, the B1 subfamily is small and comprises only 15 members, including, e.g., the secretin receptor, the glucagon receptor, and the receptors for parathyroid hormone (PTHR1 and PTHR2). The dysregulation of several family B1 receptors is involved in diseases, such as diabetes, chronic inflammation, and osteoporosis which underlines the pathophysiological importance of this GPCR subfamily. In spite of this, investigation of family B1 receptor oligomerization and especially its pharmacological importance is still at an early stage. Even though GPCR oligomerization is a well-established phenomenon, there is a need for more investigations providing a direct link between these interactions and receptor functionality in family B1 GPCRs. One example of the functional effects of GPCR oligomerization is the facilitation of allosterism including cooperativity in ligand binding to GPCRs. Here, we review the currently available data on family B1 GPCR homo- and heteromerization, mainly based on BRET investigations. Furthermore, we cover the functional influence of oligomerization on ligand binding as well as the link between oligomerization and binding cooperativity.
    Frontiers in Endocrinology 01/2012; 3:62.
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    ABSTRACT: The signaling of seven transmembrane receptors/G-protein- coupled receptors (GPCRs) is regulated by a number of receptor interacting proteins, including βarrestins (βarrs) and GPCR kinases (GRKs). In the present report, we have analyzed the interaction pattern between the glucagon-like peptide-1 (GLP-1) receptor (GLP-1R), βarr2, and GRK2 using bioluminescence resonance energy transfer assays. We found that βarr2 interacts with the GLP-1R in a biphasic manner with a phosphorylation-independent and a phosphorylation-dependent component. In competition experiments, we observed βarr2 competing with GRK2 for interaction with GLP-1R. We propose a model were βarr2 competes with GRK2 for interaction with the activated and GRK phosphorylated GLP-1R, suggesting a new role of βarr2 in regulating the orchestration of GRK2 functionality.
    Pharmacology 09/2011; 88(3-4):174-81. · 1.60 Impact Factor
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    ABSTRACT: Biological activity of the neural cell adhesion molecule (NCAM) depends on both adhesion and activation of intra-cellular signaling. Based on in vitro experiments with truncated extra-cellular domains, several models describing homophilic NCAM trans- and cis-interactions have been proposed. However, cis-dimerization in living cells has not been shown directly and the role of the cytoplasmic part in NCAM dimerization is poorly understood. Here, we used the bioluminescence resonance energy transfer (BRET(2)) technique to directly demonstrate that full-length NCAM cis-homodimerizes in living cells. Based on BRET(2)50 values we suggest that the intra-cellular part of NCAM inhibits cis-dimerization, an effect mainly dependent on the palmitoylation sites.
    FEBS letters 01/2011; 585(1):58-64. · 3.54 Impact Factor
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    ABSTRACT: To analyze the interaction between the neurokinin-1 (NK-1) receptor and G-protein coupled receptor kinases (GRKs), we performed bioluminescence resonance energy transfer(2) (BRET(2)) measurements between the family A NK-1 receptor and GRK2 and GRK5 as well as their respective kinase-inactive mutants. We observed agonist induced interaction of both GRK5 and GRK2 with the activated NK-1 receptor. In saturation experiments, we observed GRK5 to interact with the activated receptor in a monophasic manner while GRK2 interacted in a biphasic manner with the low affinity phase corresponding to receptor affinity for GRK5. Agonist induced GRK5 interaction with the receptor was dependent on intact kinase-activity, whereas the high affinity phase of GRK2 interaction was independent of kinase activity. We were surprised to find that the BRET(2) saturation experiments indicated that before receptor activation, the full-length NK-1 receptor, but not a functional C-terminal tail-truncated receptor, is preassociated with GRK5 in a relatively low-affinity state. We demonstrate that GRK5 can compete for agonist induced GRK2 interaction with the NK-1 receptor, whereas GRK2 does not compete for receptor interaction with GRK5. We suggest that GRK5 is preassociated with the NK-1 receptor and that GRK5, rather than GRK2, is a key player in competitive regulation of GRK subtype specific interaction with the NK-1 receptor.
    Molecular pharmacology 03/2008; 73(2):349-58. · 4.53 Impact Factor
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    ABSTRACT: The glucagon-like peptide (GLP)-1 receptor is a promising target for the treatment of type 2 diabetes and obesity, and there is great interest in characterizing the pharmacology of the GLP-1 receptor and its ligands. In the present report, we have applied bioluminescence resonance energy transfer assays to measure agonist-induced recruitment of betaarrestins and G-protein-coupled receptor kinase (GRK) 2 to the GLP-1 receptor in addition to traditional measurements of second messenger generation. The peptide hormone oxyntomodulin is described in the literature as a full agonist on the glucagon and GLP-1 receptors. Surprisingly, despite being full agonists in GLP-1 receptor-mediated cAMP accumulation, oxyntomodulin and glucagon were observed to be partial agonists in recruiting betaarrestins and GRK2 to the GLP-1 receptor. We suggest that oxyntomodulin and glucagon are biased ligands on the GLP-1 receptor.
    Journal of Pharmacology and Experimental Therapeutics 07/2007; 322(1):148-54. · 3.89 Impact Factor
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    ABSTRACT: Members of the family of adenosine deaminases acting on RNA (ADARs) can catalyze the hydrolytic deamination of adenosine to inosine and thereby change the sequence of specific mRNAs with highly double-stranded structures. The ADARs all contain one or more repeats of the double-stranded RNA binding motif (DRBM). By both in vitro and in vivo assays, we show that the DRBMs of rat ADAR2 are necessary and sufficient for dimerization of the enzyme. Bioluminescence resonance energy transfer (BRET) demonstrates that ADAR2 also exists as dimers in living mammalian cells and that mutation of DRBM1 lowers the dimerization affinity while mutation of DRBM2 does not. Nonetheless, the editing efficiency of the GluR2 Q/R site depends on a functional DRBM2. The ADAR2 DRBMs thus serve differential roles in RNA dimerization and GluR2 Q/R editing, and we propose a model for RNA editing that incorporates the new findings.
    RNA 08/2006; 12(7):1350-60. · 5.09 Impact Factor
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    ABSTRACT: Much evidence indicates that, during activation of seven-transmembrane (7TM) receptors, the intracellular segments of the transmembrane helices (TMs) move apart with large amplitude, rigid body movements of especially TM-VI and TM-VII. In this study, AspIII:08 (Asp113), the anchor point for monoamine binding in TM-III, was used as the starting point to engineer activating metal ion sites between the extracellular segments of the beta2-adrenergic receptor. Cu(II) and Zn(II) alone and in complex with aromatic chelators acted as potent (EC50 decreased to 0.5 microm) and efficacious agonists in sites constructed between positions III:08 (Asp or His), VI:16 (preferentially Cys), and/or VII:06 (preferentially Cys). In molecular models built over the backbone conformation of the inactive rhodopsin structure, the heavy atoms that coordinate the metal ion were located too far away from each other to form high affinity metal ion sites in both the bidentate and potential tridentate settings. This indicates that the residues involved in the main ligand-binding pocket will have to move closer to each other during receptor activation. On the basis of the distance constraints from these activating metal ion sites, we propose a global toggle switch mechanism for 7TM receptor activation in which inward movement of the extracellular segments of especially TM-VI and, to some extent, TM-VII is coupled to the well established outward movement of the intracellular segments of these helices. We suggest that the pivots for these vertical seesaw movements are the highly conserved proline bends of the involved helices.
    Journal of Biological Chemistry 07/2006; 281(25):17337-46. · 4.65 Impact Factor
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    ABSTRACT: Numerous studies have attested to the importance of the extreme C terminus of G protein alpha subunits in determining their selectivity of receptor recognition. We have previously reported that a highly conserved glycine residue within linker I is important for constraining the fidelity of receptor recognition by Galpha(q) proteins. Herein, we explored whether both modules (linker I and extreme C terminus) interact cooperatively in switching G protein-coupled receptor (GPCR)-to-effector specificity and created as models mutant Galpha(q) proteins in which glycine was replaced with various amino acids and the C-terminal five Galpha(q) residues with the corresponding Galpha(i) or Galpha(s) sequence. Coupling properties of the mutated Galpha(q) proteins were determined after coexpression with a panel of 13 G(i)-and G(s) -selective receptors and compared with those of Galpha proteins modified in only one module. Galpha proteins modified in both modules are significantly more efficacious in channeling non-G(q) -selective receptors to G(q)-mediated signaling events compare with those containing each module alone. Additive effects of both modules were observed even if individual modules lacked an effect on GPCR-to-effector specificity. Dually modified Galpha proteins were also superior in conferring high-affinity agonist sites onto a coexpressed GPCR in the absence, but not in the presence, of guanine nucleotides. Together, our data suggest that receptor-G protein coupling selectivity involves cooperative interactions between the extreme C terminus and linker I of Galpha proteins and that distinct determinants of selectivity exist for individual receptors.
    Journal of Pharmacology and Experimental Therapeutics 05/2005; 313(1):78-87. · 3.89 Impact Factor
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    ABSTRACT: To dissect the interaction between beta-arrestin ((beta)arr) and family B G protein-coupled receptors, we constructed fusion proteins between the glucagon-like peptide 1 receptor and (beta)arr2. The fusion constructs had an increase in apparent affinity selectively for glucagon, suggesting that (beta)arr2 interaction locks the receptor in a high-affinity conformation, which can be explored by some, but not all, ligands. The fusion constructs adopted a signaling phenotype governed by the tethered (beta)arr2 with an attenuated G protein-mediated cAMP signal and a higher maximal internalization compared with wild-type receptors. This distinct phenotype of the fusion proteins can not be mimicked by coexpressing wild-type receptor with (beta)arr2. However, when the wild-type receptor was coexpressed with both (beta)arr2 and G protein-coupled receptor kinase 5, a phenotype similar to that observed for the fusion constructs was observed. We conclude that the glucagon-like peptide 1 fusion construct mimics the natural interaction of the receptor with (beta)arr2 with respect to binding peptide ligands, G protein-mediated signaling and internalization, and that this distinct molecular phenotype is reminiscent of that which has previously been characterized for family A G protein-coupled receptors, suggesting similarities in the effect of (beta)arr interaction between family A and B receptors also at the molecular level.
    Molecular Endocrinology 04/2005; 19(3):812-23. · 4.75 Impact Factor
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    ABSTRACT: Several domains of G protein alpha subunits are implicated in the control of receptor-G protein coupling specificity. Among these are the extreme N-and C-termini, the alpha4/beta6-loops, and the loop linking the N-terminal alpha-helix to the beta1-strand of the ras-like domain. In this study, we illustrate that single-point mutations of a highly conserved glycine residue within the linker I region of the Galpha(q) subunit confers upon the mutant Galpha(q) the ability to be activated by Galpha(i)- and Galpha(s) -coupled receptors, as evidenced by guanosine 5'-O-(3-[(35)S]thio)triphosphate binding and inositol phosphate turnover assays. The mutations did not affect expression of Galpha(q) proteins nor their ability to stimulate phospholipase Cbeta. It is noteworthy that both mutant and wild-type Galpha(q) proteins are indistinguishable in their ability to reconstitute a functional Gq-PLCbeta-calcium signaling pathway when cotransfected with the Galpha(q)-coupled neurokinin 1 or muscarinic M3 receptor into mouse embryonic fibroblasts derived from Galpha(q/11) knockout mice. On a three-dimensional model of the receptor-G protein complex, the highly conserved linker I region connecting the helical and the GTPase domain of the Galpha protein is inaccessible to the intracellular surface of the receptors. Our data indicate that receptor-G protein coupling specificity is not exclusively governed by direct receptor-G protein interaction and that it even bypasses the requirement of the extreme C terminus of Galpha, a well accepted receptor recognition domain, suggesting a novel allosteric mechanism for G protein-coupled receptor-G protein selectivity.
    Molecular Pharmacology 09/2004; 66(2):250-9. · 4.41 Impact Factor
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    ABSTRACT: This study has focused on enhancing the signal generated from the interaction between a G-protein-coupled receptor (GPCR) and beta-arrestin 2 (beta-arr2), measured by the bioluminescence resonance energy transfer (BRET(2)) technology. Both class A (beta(2)-adrenergic receptor [beta(2)-AR]) and class B (neurokinin-type 1 receptor [NK1-R]) GPCRs, classified based on their internalization characteristics, have been analyzed. It was evaluated whether the BRET(2) signal can be enhanced by using (1) beta-arr2 phosphorylation-independent mutant (beta-arr2 R169E) and (2) beta-arr2 mutants deficient in their ability to interact with the components of the clathrin-coated vesicles (beta-arr2 R393E, R395E and beta-arr2 373 stop). For the class B receptor, there was no major difference in the agonist-promoted BRET(2) signal when comparing results obtained with wild-type (wt) and mutant beta-arr2. However, with the class A receptor, a more than 2-fold increase in the BRET(2) signal was observed with beta-arr2 mutants lacking the AP-2 or both AP-2 and clathrin binding sites. This set of data suggests that the inability of these beta-arr2 mutants to interact with the components of the clathrin-coated vesicle probably prevents their rapid dissociation from the receptor, thus yielding an increased and more stable BRET(2) signal. The beta-arr2 R393E, R395E mutant also enhanced the signal window with other members of the GPCR family (neuropeptide Y type 2 receptor [NPY2-R] and TG1019 receptor) and was successfully applied in full-plate BRET(2)-based agonist and antagonist screening assays.
    Journal of Biomolecular Screening 07/2004; 9(4):322-33. · 2.21 Impact Factor