TY - JOUR A1 - Steinmetzger, Christian A1 - Bessi, Irene A1 - Lenz, Ann-Kathrin A1 - Höbartner, Claudia T1 - Structure-fluorescence activation relationships of a large Stokes shift fluorogenic RNA aptamer JF - Nucleic Acids Research N2 - The Chili RNA aptamer is a 52 nt long fluorogen-activating RNA aptamer (FLAP) that confers fluorescence to structurally diverse derivatives of fluorescent protein chromophores. A key feature of Chili is the formation of highly stable complexes with different ligands, which exhibit bright, highly Stokes-shifted fluorescence emission. In this work, we have analyzed the interactions between the Chili RNA and a family of conditionally fluorescent ligands using a variety of spectroscopic, calorimetric and biochemical techniques to reveal key structure - fluorescence activation relationships (SFARs). The ligands under investigation form two categories with emission maxima of ~540 nm or ~590 nm, respectively, and bind with affinities in the nanomolar to low-micromolar range. Isothermal titration calorimetry was used to elucidate the enthalpic and entropic contributions to binding affinity for a cationic ligand that is unique to the Chili aptamer. In addition to fluorescence activation, ligand binding was also observed by NMR spectroscopy, revealing characteristic signals for the formation of a G-quadruplex only upon ligand binding. These data shed light on the molecular features required and responsible for the large Stokes shift and the strong fluorescence enhancement of red and green emitting RNA-chromophore complexes. KW - Chili RNA Aptamer KW - fluorogen-activating RNA aptamer (FLAP) KW - Stokes-shifted fluorescence emission KW - key structure - fluorescence activation relationships (SFARs) KW - ligand binding Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-192340 ER - TY - JOUR A1 - Capra, Valérie A1 - Busnelli, Marta A1 - Perenna, Alessandro A1 - Ambrosio, Manuela A1 - Accomazzo, Maria Rosa A1 - Galés, Celine A1 - Chini, Bice A1 - Rovati, G. Enrico T1 - Full and Partial Agonists of Thromboxane Prostanoid Receptor Unveil Fine Tuning of Receptor Superactive Conformation and G Protein Activation JF - PLoS ONE N2 - The intrahelical salt bridge between \(E/D^{3.49}\) and \(R^{3.50}\) within the E/DRY motif on helix 3 (H3) and the interhelical hydrogen bonding between the E/DRY and residues on H6 are thought to be critical in stabilizing the class A G protein-coupled receptors in their inactive state. Removal of these interactions is expected to generate constitutively active receptors. This study examines how neutralization of \(E^{3.49/6.30}\) in the thromboxane prostanoid (TP) receptor alters ligand binding, basal, and agonist-induced activity and investigates the molecular mechanisms of G protein activation. We demonstrate here that a panel of full and partial agonists showed an increase in affinity and potency for E129V and E240V mutants. Yet, even augmenting the sensitivity to detect constitutive activity (CA) with overexpression of the receptor or the G protein revealed resistance to an increase in basal activity, while retaining fully the ability to cause agonist-induced signaling. However, direct G protein activation measured through bioluminescence resonance energy transfer (BRET) indicates that these mutants more efficiently communicate and/or activate their cognate G proteins. These results suggest the existence of additional constrains governing the shift of TP receptor to its active state, together with an increase propensity of these mutants to agonist-induced signaling, corroborating their definition as superactive mutants. The particular nature of the TP receptor as somehow "resistant" to CA should be examined in the context of its pathophysiological role in the cardiovascular system. Evolutionary forces may have favored regulation mechanisms leading to low basal activity and selected against more highly active phenotypes. KW - coupled receptor KW - ligand binding KW - intracellular loop KW - molecular dynamics KW - Beta(1)-adrenergic receptor KW - ionic look KW - Beta(2)-adrenergic receptor KW - crystal structure KW - constitutive activity Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-131013 VL - 8 IS - 3 ER - TY - JOUR A1 - Diestel, Uschi A1 - Resch, Marcus A1 - Meinhardt, Kathrin A1 - Weiler, Sigrid A1 - Hellmann, Tina V. A1 - Mueller, Thomas D. A1 - Nickel, Joachim A1 - Eichler, Jutta A1 - Muller, Yves A. T1 - Identification of a Novel TGF-beta-Binding Site in the Zona Pellucida C-terminal (ZP-C) Domain of TGF-\(\beta\)-Receptor-3 (TGFR-3) JF - PLoS ONE N2 - The zona pellucida (ZP) domain is present in extracellular proteins such as the zona pellucida proteins and tectorins and participates in the formation of polymeric protein networks. However, the ZP domain also occurs in the cytokine signaling co-receptor transforming growth factor beta (TGF-\(\beta\)) receptor type 3 (TGFR-3, also known as betaglycan) where it contributes to cytokine ligand recognition. Currently it is unclear how the ZP domain architecture enables this dual functionality. Here, we identify a novel major TGF-beta-binding site in the FG loop of the C-terminal subdomain of the murine TGFR-3 ZP domain (ZP-C) using protein crystallography, limited proteolysis experiments, surface plasmon resonance measurements and synthetic peptides. In the murine 2.7 angstrom crystal structure that we are presenting here, the FG-loop is disordered, however, well-ordered in a recently reported homologous rat ZP-C structure. Surprisingly, the adjacent external hydrophobic patch (EHP) segment is registered differently in the rat and murine structures suggesting that this segment only loosely associates with the remaining ZP-C fold. Such a flexible and temporarily-modulated association of the EHP segment with the ZP domain has been proposed to control the polymerization of ZP domain-containing proteins. Our findings suggest that this flexibility also extends to the ZP domain of TGFR-3 and might facilitate co-receptor ligand interaction and presentation via the adjacent FG-loop. This hints that a similar C-terminal region of the ZP domain architecture possibly regulates both the polymerization of extracellular matrix proteins and cytokine ligand recognition of TGFR-3. KW - coreceptor KW - receptor type III KW - growth factor beta KW - ligand binding KW - betaglycan KW - proteins KW - mutagenesis KW - polymerization KW - glycoprotein KW - superfamily Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-130904 VL - 8 IS - 6 ER -