Traumatic brain injury (TBI) is a leading cause of death and long-term disability worldwide, and survivors are often left with cognitive deficits and significant problems with day to day tasks. To date, therapeutic pharmacological treatments of TBI remain elusive despite numerous clinical trials. An improved understanding of the molecular and cellular response to injury may help guide future treatment strategies. One promising marker for brain injury is the translocator protein (TSPO), which is normally expressed at a low level, but is highly expressed following brain damage and is associated with neuroinflammation. The isoquinoline carboxamide PK11195 binds selectively to the TSPO in many species, and has therefore become the most-studied TSPO ligand. To characterize the time-course of TSPO expression in the controlled cortical injury (CCI) model of TBI we subjected Sprague-Dawley rats to CCI and euthanatized them after 30 minutes, 12 hours, 1, 2, 4, or 6 days. Autoradiography with radiolabelled PK11195 was used to assess the time-course of TSPO binding following CCI. Autoradiographs were compared to adjacent tissue slices stained with the microglia/macrophage marker ED-1, with which a moderate positive correlation was discovered. PK11195 autoradiography was used as a tool with which to assess neuroinflammation following CCI and the administration of an α7 nAChR antagonist, methyllycaconitine (MLA). We hypothesized that blocking the calcium permeable α7 nAChR after brain injury would have a neuroprotective effect by attenuating excitotoxicity in the shortterm. Our study revealed clear dose-dependent tissue sparing in rats administered MLA after trauma and a modest improvement in functional outcome. The relatively modest recovery of function with MLA, which could be due to prolonged α7 nAChR blockade or downregulation lead us to explore the potential of α7 nAChR partial agonists in treating TBI. The α7 nAChR partial agonists tropisetron, ondansetron, and DMXB-A produced a moderate attenuation of cognitive deficits, but did not have a neuroprotective effect on tissue sparing. These studies show that following TBI, α7 nAChR modulation can have neuroprotective effects and attenuate cognitive deficits. Whether this modulation is best achieved through partial agonist treatment alone or a combination antagonist/agonist treatment remains to be determined.

Os receptores nucleares compreendem uma superfamília de proteínas intracelulares reguladas relacionados estruturalmente, capazes de reconhecer sequências específicas de DNA e regulam a transcrição de genes alvos respondendo a sinais metabólicos, hormônios e outras moléculas regulatórias integrando muitas vias de sinalização. Os receptores ativadores da proliferação de peroxissomos (PPARs) são receptores nucleares que regem a transcrição de vários genes envolvidos principalmente no metabolismo de ácidos graxos e energia. A ativação do PPARY possui um amplo aspecto de funções biológicas, regulando o metabolismo, reduzindo a inflamação, influenciando o equilíbrio das células imunes, inibindo a apoptose e o estresse oxidativo e melhorando a função endotelial. Estes efeitos parecem ser benéficos não apenas em diabetes e aterosclerose, mas também em várias outras condições. Os agonistas do PPARY são utilizados como sensibilizadores de insulina para o tratamento da diabetes II, sendo um alvo molecular dos fármacos tiazolidinadionas. Diversos efeitos colaterais severos associados ao uso dos fármacos desta classe e à importância do PPARY no metabolismo de glicose e na sensibilização da insulina, o presente trabalho justifica-se como um esforço para avançar na compreensão da interação entre ligantes sintéticos com o receptor PPARY e a proposição de moléculas mais seguras e mais eficazes para a manutenção de níveis euglicêmicos. Foi realizada a expressão, a purificação, seguida de estudos cristalográficos em cinco ligantes selecionados a partir de etapas de docking realizados anteriormente pelo nosso grupo de Biotecnologia Molecular do Instituto de Física de São Carlos. Os ensaios de cristalização do PPARY complexado a ligantes sintéticos resultaram em duas estruturas cristalográficas que apresentaram uma conformação em que os ligantes não interagiram diretamente na hélice 12 como descritos para agonistas totais do PPARY, adotando características de agonistas parciais. Esses ligantes apresentaram interações hidrofóbicas que estabilizam as fitas-β. Este conjunto de informações estruturais apresentados neste trabalho para o PPARY proporcionou um entendimento das interações que esse receptor é capaz de fazer na presença de um ligante, além de que poderão ser úteis no desenvolvimento de novos moduladores seletivos do PPARY semelhante ao que já se encontram no mercado, porém com efeitos colaterais reduzidos. / Nuclear receptors comprise a superfamily of structurally-related regulated intracellular proteins capable of recognizing specific DNA sequences and regulating the transcription of target genes responding to metabolic signals, hormones and other regulatory molecules integrating many signaling pathways. Peroxisome proliferator-activating receptors (PPARs) are nuclear receptors that govern the transcription of several genes involved primarily in fatty acid and energy metabolism. Activation of PPARY has a broad aspect of biological functions, regulating metabolism, reducing inflammation, influencing immune cell balance, inhibiting apoptosis and oxidative stress, and improving endothelial function. These effects appear to be beneficial not only in diabetes and atherosclerosis, but also in several other conditions. PPARY agonists are used as insulin sensitizers for the treatment of diabetes II, being a molecular target of the thiazolidinediones drugs. A number of severe side effects associated with the use of drugs of this class and the importance of PPARY in glucose metabolism and insulin sensitization, the present work is justified as an effort to advance the understanding of the interaction between synthetic ligands with the PPARY receptor and proposing safer and more effective molecules for the maintenance of euglycemic levels. The expression, purification, followed by crystallographic studies in five ligands selected from docking steps previously performed by our Molecular Biotechnology group of the Physics Institute of São Carlos. The crystallization assays of PPARY complexed to synthetic ligands resulted in two crystallographic structures that exhibited a conformation in which the ligands did not interact directly in helix 12 as described for total PPARY agonists, adopting characteristics of partial agonists. These ligands showed hydrophobic interactions that stabilize the β-ribbons. This set of structural information presented in this work for the PPARY was of great value for the understanding of the interactions that this receptor is able to make in the presence of a ligand, besides that they could be useful in the development of new selective modulators of the PPARY similar to that are already on the market, but with reduced side effects.

Os receptores nucleares compreendem uma superfamília de proteínas intracelulares reguladas relacionados estruturalmente, capazes de reconhecer sequências específicas de DNA e regulam a transcrição de genes alvos respondendo a sinais metabólicos, hormônios e outras moléculas regulatórias integrando muitas vias de sinalização. Os receptores ativadores da proliferação de peroxissomos (PPARs) são receptores nucleares que regem a transcrição de vários genes envolvidos principalmente no metabolismo de ácidos graxos e energia. A ativação do PPARY possui um amplo aspecto de funções biológicas, regulando o metabolismo, reduzindo a inflamação, influenciando o equilíbrio das células imunes, inibindo a apoptose e o estresse oxidativo e melhorando a função endotelial. Estes efeitos parecem ser benéficos não apenas em diabetes e aterosclerose, mas também em várias outras condições. Os agonistas do PPARY são utilizados como sensibilizadores de insulina para o tratamento da diabetes II, sendo um alvo molecular dos fármacos tiazolidinadionas. Diversos efeitos colaterais severos associados ao uso dos fármacos desta classe e à importância do PPARY no metabolismo de glicose e na sensibilização da insulina, o presente trabalho justifica-se como um esforço para avançar na compreensão da interação entre ligantes sintéticos com o receptor PPARY e a proposição de moléculas mais seguras e mais eficazes para a manutenção de níveis euglicêmicos. Foi realizada a expressão, a purificação, seguida de estudos cristalográficos em cinco ligantes selecionados a partir de etapas de docking realizados anteriormente pelo nosso grupo de Biotecnologia Molecular do Instituto de Física de São Carlos. Os ensaios de cristalização do PPARY complexado a ligantes sintéticos resultaram em duas estruturas cristalográficas que apresentaram uma conformação em que os ligantes não interagiram diretamente na hélice 12 como descritos para agonistas totais do PPARY, adotando características de agonistas parciais. Esses ligantes apresentaram interações hidrofóbicas que estabilizam as fitas-β. Este conjunto de informações estruturais apresentados neste trabalho para o PPARY proporcionou um entendimento das interações que esse receptor é capaz de fazer na presença de um ligante, além de que poderão ser úteis no desenvolvimento de novos moduladores seletivos do PPARY semelhante ao que já se encontram no mercado, porém com efeitos colaterais reduzidos. / Nuclear receptors comprise a superfamily of structurally-related regulated intracellular proteins capable of recognizing specific DNA sequences and regulating the transcription of target genes responding to metabolic signals, hormones and other regulatory molecules integrating many signaling pathways. Peroxisome proliferator-activating receptors (PPARs) are nuclear receptors that govern the transcription of several genes involved primarily in fatty acid and energy metabolism. Activation of PPARY has a broad aspect of biological functions, regulating metabolism, reducing inflammation, influencing immune cell balance, inhibiting apoptosis and oxidative stress, and improving endothelial function. These effects appear to be beneficial not only in diabetes and atherosclerosis, but also in several other conditions. PPARY agonists are used as insulin sensitizers for the treatment of diabetes II, being a molecular target of the thiazolidinediones drugs. A number of severe side effects associated with the use of drugs of this class and the importance of PPARY in glucose metabolism and insulin sensitization, the present work is justified as an effort to advance the understanding of the interaction between synthetic ligands with the PPARY receptor and proposing safer and more effective molecules for the maintenance of euglycemic levels. The expression, purification, followed by crystallographic studies in five ligands selected from docking steps previously performed by our Molecular Biotechnology group of the Physics Institute of São Carlos. The crystallization assays of PPARY complexed to synthetic ligands resulted in two crystallographic structures that exhibited a conformation in which the ligands did not interact directly in helix 12 as described for total PPARY agonists, adopting characteristics of partial agonists. These ligands showed hydrophobic interactions that stabilize the β-ribbons. This set of structural information presented in this work for the PPARY was of great value for the understanding of the interactions that this receptor is able to make in the presence of a ligand, besides that they could be useful in the development of new selective modulators of the PPARY similar to that are already on the market, but with reduced side effects.

The glycine receptor (GlyR) is a ligand-gated ion channel member of the cys-loop receptor superfamily, responsible for inhibitory neurotransmission in the brain and spinal cord. Both glycine and the partial agonist taurine act as endogenous ligands of the GlyR. Taurine-activated GlyR may have a role in the rewarding effects of drugs of abuse, such as ethanol. As a partial agonist, taurine has a decreased efficacy relative to glycine, resulting in a decreased maximum response. We investigated the effects of ethanol, anesthetics, inhalants, and zinc to determine if these allosteric modulators could increase the efficacy of the taurine-activated GlyR. Whole cell recordings of wild type GlyR revealed that each of the allosteric modulators potentiated currents generated by saturating concentrations of taurine but not glycine, implying an increase in efficacy. Zinc is found at GlyR-potentiating concentrations throughout the nervous system, so we examined the combinatorial effects of these allosteric modulators with zinc to mimic in vivo conditions. Whole cell recordings revealed that zinc potentiation of saturating taurine-generated currents decreased further potentiation by another allosteric modulator, indicating no synergistic effects on efficacy. We next investigated the actions of ethanol and isoflurane on the taurine-activated GlyR at the single channel level, finding that both allosteric modulators stabilized the channel open state, increasing the efficacy of the taurine-activated GlyR. We previously identified a mutation in the ligand-binding domain of the GlyR (D97R) that produces spontaneously activating channels, on which taurine has increased efficacy. We identified a residue, R131, as a possible binding partner of D97 in forming an electrostatic interaction that holds the channel in the closed state. We found that disruption of this interaction results in greatly increased taurine efficacy, indicating that efficacy for partial agonists may be determined by agonist ability to break this bond early in the activation process following binding. Thus we find differential mechanisms of allosteric modulation and efficacy determinations for the GlyR when activated by taurine vs. glycine. / text

The glycine receptor (GlyR) is a ligand-gated ion channel member of the cys-loop receptor superfamily, responsible for inhibitory neurotransmission in the brain and spinal cord. Both glycine and the partial agonist taurine act as endogenous ligands of the GlyR. Taurine-activated GlyR may have a role in the rewarding effects of drugs of abuse, such as ethanol. As a partial agonist, taurine has a decreased efficacy relative to glycine, resulting in a decreased maximum response. We investigated the effects of ethanol, anesthetics, inhalants, and zinc to determine if these allosteric modulators could increase the efficacy of the taurine-activated GlyR. Whole cell recordings of wild type GlyR revealed that each of the allosteric modulators potentiated currents generated by saturating concentrations of taurine but not glycine, implying an increase in efficacy. Zinc is found at GlyR-potentiating concentrations throughout the nervous system, so we examined the combinatorial effects of these allosteric modulators with zinc to mimic in vivo conditions. Whole cell recordings revealed that zinc potentiation of saturating taurine-generated currents decreased further potentiation by another allosteric modulator, indicating no synergistic effects on efficacy. We next investigated the actions of ethanol and isoflurane on the taurine-activated GlyR at the single channel level, finding that both allosteric modulators stabilized the channel open state, increasing the efficacy of the taurine-activated GlyR. We previously identified a mutation in the ligand-binding domain of the GlyR (D97R) that produces spontaneously activating channels, on which taurine has increased efficacy. We identified a residue, R131, as a possible binding partner of D97 in forming an electrostatic interaction that holds the channel in the closed state. We found that disruption of this interaction results in greatly increased taurine efficacy, indicating that efficacy for partial agonists may be determined by agonist ability to break this bond early in the activation process following binding. Thus we find differential mechanisms of allosteric modulation and efficacy determinations for the GlyR when activated by taurine vs. glycine. / text

Rhodopsin, der Rezeptor der visuellen Kaskade, gehört zu größten Klasse A der G-Protein-koppelnden Rezeptoren (GPCRs) und gilt als Modell-Rezeptor in der GPCR-Forschung. Über 3 % des humanen Genoms kodieren für GPCRs, doch trotz der physiologischen Bedeutung dieser Proteinfamilie sind die fundamentalen Mechanismen, mit denen diese Rezeptoren extrazelluläre Signale in das Zellinnere weiterleiten noch nicht verstanden. In der vorliegenden Dissertation werden Aspekte des Aktivierungsmechanismus von Rhodopsin sowie der Kopplung und Aktivierung des G-Proteins Transduzin untersucht. Die Arbeit ist in drei Schwerpunkte unterteilt: I. Es wurde ein in GPCR’s hochkonserviertes NPxxYx(5,6)F Motiv (Aminosäuresequenz Asn-Pro-x-x-Tyr-x(5,6)-Phe) in der siebten und achten Helix charakterisiert. In diesem konservierten Motiv sind mehrere für die Ausbildung der aktiven Rezeptorkonformation wichtige Funktionen vereint: Verknüpfung zu einem Wasserstoffbrückennetzwerk, Helixflexibilität sowie die exakte Positionierung der achten Helix. Letzteres hat nicht nur bei der Rezeptoraktivierung sondern auch bei der nachfolgenden Interaktion mit dem G-Protein eine Bedeutung. II. Anhand von chimären Rezeptoren, bei denen Teile der achten Helix durch homologe Sequenzen des beta2-adrenergen Rezeptors ausgetauscht wurden, wurde die Rolle der achten Helix bei der Rezeptor-Aktivierung und Bindung des G-Proteins untersucht. Auch bei dieser Studie wurde gezeigt, dass die exakte Positionierung der achten Helix essentiell für die Interaktion mit dem G-Protein ist. Zudem wurde ein bezüglich der G-Protein-Aktivierung funktionsfähiger chimärer Rezeptor gefunden, was auf einen übergeordneten Mechanismus bei der Aktivierung von G-Proteinen durch GPCRs hindeutet. III. Die Funktion des ß-Ionon-Rings des Retinals beim Aktivierungsmechanismus von Rhodopsin wurde an einem Retinal studiert, bei welchem Teile des Retinal-Rings fehlten (azyklisches Retinal). Auch diesem azyklischen Retinal können Eigenschaften eines partiellen Agonisten zugeschrieben werden. Beim Vergleich zu Pigmenten mit dem nativen 11-cis-Retinal wurden starke Analogien bei der initialen Energieaufnahme durch die Retinal-Isomerisierung sowie bei der Weiterleitung der Lichtenergie ins Protein gefunden. Allerdings wird die Energie schlechter auf das Protein übertragen, wodurch wesentlich weniger der aktiven G-Protein bindenden Rezeptorkonformation gebildet wird. Als wichtigste Funktion des Retinal-Rings wurde die Aufrechterhaltung der aktiven Meta-II-Konformation identifiziert. / Rhodopsin, the receptor of the visual cascade, belongs to the largest group A of G-protein coupled receptors (GPCRs) and can be seen as a model receptor in GPCR research. More than 3 % of the human genome code for GPCRs. But despite their physiological relevance, the detailed mechanism of signal transduction from extra cellular signal to different cellular pathways remains to be fully understood. Different aspects of receptor activation and the coupling and activation of the G-protein transducin are investigated in this dissertation. The thesis focuses on the following three subjects: I. A NPxxYx(5,6)F motif (amino acid sequence Asn-Pro-x-x-Tyr-x(5,6)-Phe) has been characterized for rhodopsin. It is localized in helix VII and VIII and is highly conserved throughout the GPCR family. Various roles for rhodopsin activation are combined in this motif: linkage to a hydrogen-bond network, helix flexibility and the exact positioning of helix VIII. The latter is not only relevant for the activation of the receptor but also for interaction with its G-protein. II. The role of helix VIII for receptor activation and G-protein coupling was studied on chimeric receptors, in which parts of helix VIII were exchanged against homologous sequences of the beta2 adrenergic receptor. This study confirmed the importance of helix VIII’s position for G-protein coupling. Furthermore, a chimeric receptor was found, which was fully functional concerning G-protein activation. This indicates that GPCRs might use a single, generic mechanism for G-protein activation. III. The role of the ß-ionone-ring for the activation mechanism of rhodopsin was studied by means of an acyclic retinal, which lacks four carbon atoms of the ß-ionone-ring. This modified retinal could be classified as a partial agonist for rhodopsin. Energy input by retinal isomerization and formation of the G-protein binding Meta-II conformation were found to be very similar to rhodopsin when bound to its native 11-cis-retinal. However, the lack of the ring structure resulted in a lower amount of Meta-II and a fast decay of activity. It was concluded that the main role of the ring structure is to maintain the active state of rhodopsin.