The change of day and night is one of the challenges all organisms are exposed to, as they have to adjust their physiology and behavior in an appropriate way. Therefore so called circadian clocks have evolved, which allow the organism to predict these cyclic changes of day and night. The underlying molecular mechanism is oscillating with its endogenous period of approximately 24 hours in constant conditions, but as soon as external stimuli, so called Zeitgebers, are present, the clocks adjust their period to exactly 24h, which is called entrainment. Studies in several species, including humans, animals and plants, showed that light is the most important Zeitgeber synchronizing physiology and behavior to the changes of day and night. Nevertheless also other stimuli, like changes in temperature, humidity or social interactions, are powerful Zeitgebers for entraining the clock. This thesis will focus on the question, how light influences the locomotor behavior of the fly in general, including a particular interest on the entrainment of the circadian clock. As a model organism Drosophila melanogaster was used. During the last years several research groups investigated the effect of light on the circadian clock and their results showed that several light input pathways to the clock contribute to wild-type behavior. Most of the studies focused on the photopigment Cryptochrome (CRY) which is expressed in about half of the 150 clock neurons in the fly. CRY is activated by light, degrades the clock protein Timeless (TIM) and hence entrains the clock to the light-dark (LD)-cycle resulting from changes of day and night. However, also flies lacking CRY are still able to entrain their clock mechanism as well as their activity-rest-rhythm to LD-cycles, clearly showing that the visual system of the fly also contributes to clock synchronization. The mechanism how light information from the visual system is transferred to the clock is so far still unknown. This is also true for so-called masking-effects which are changes in the behavior of the animal that are directly initiated by external stimuli and therefore independent of the circadian clock. These effects complement the behavior of the animals as they enable the fly to react quickly to changes in the environment even during the clock-controlled rest state. Both of these behavioral features were analyzed in more detail in this study. On the one hand, we investigated the influence of the compound eyes on the entrainment of the clock neurons and on the other hand, we tried to separate clock-controlled behavior from masking. To do so "nature-like" light conditions were simulated allowing the investigation of masking and entrainment within one experiment. The simulation of moonlight and twilight conditions caused significant changes in the locomotor behavior. Moonlit nights increased nocturnal activity levels and shifted the morning (M) and evening (E) activity bouts into the night. The opposite was true for the investigation of twilight, as the activity bouts were shifted into the day. The simulation of twilight and moonlight within the same experiment further showed that twilight appears to dominate over moonlight, which is in accordance to the assumption that twilight in nature is one of the key signals to synchronize the clock as the light intensity during early dawn rises similarly in every season. By investigating different mutants with impaired visual system we showed that the compound eyes are essential for the observed behavioral adaptations. The inner receptor cells (R7 and R8) are important for synchronizing the endogenous clock mechanism to the changes of day and night. In terms of masking, a complex interaction of all receptor cells seems to adjust the behavioral pattern, as only flies lacking photopigments in inner and outer receptor cells lacked all masking effects. However, not only the compound eyes seem to contribute to rhythmic activity in moonlit nights. CRY-mutant flies shift their E activity bout even more into the night than wild-type flies do. By applying Drosophila genetics we were able to narrow down this effect to only four CRY expressing clock neurons per hemisphere. This implies that the compound eyes and CRY in the clock neurons have antagonistic effects on the timing of the E activity bout. CRY advances activity into the day, whereas the compound eyes delay it. Therefore, wild-type behavior combines both effects and the two light inputs might enable the fly to time its activity to the appropriate time of day. But CRY expression is not restricted to the clock neurons as a previous study showed a rather broad distribution within the compound eyes. In order to investigate its function in the eyes we collaborated with Prof. Rodolfo Costa (University of Padova). In our first study we were able to show that CRY interacts with the phototransduction cascade and thereby influences visual behavior like phototaxis and optomotor response. Our second study showed that CRY in the eyes affects locomotor activity rhythms. It appears to contribute to light sensation without being a photopigment per se. Our results rather indicate that CRY keeps the components of the phototransduction cascade close to the cytoskeleton, as we identified a CRY-Actin interaction in vitro. It might therefore facilitate the transformation of light energy into electric signals. In a further collaboration with Prof. Orie Shafer (University of Michigan) we were able to shed light on the significance of the extraretinal Hofbauer-Buchner eyelet for clock synchronization. Excitation of the eyelet leads to Ca2+ and cAMP increases in specific clock neurons, consequently resulting in a shift of the flies´ rhythmic activity. Taken together, the experiments conducted in this thesis revealed new functions of different eye structures and CRY for fly behavior. We were furthermore able to show that masking complements the rhythmic behavior of the fly, which might help to adapt to natural conditions. / Der Wechsel von Tag und Nacht stellt für viele Organismen eine große Herausforderung dar, da sie ihre Physiologie und auch das Verhalten den äußeren Gegebenheiten anpassen müssen. Um dieser Aufgabe gerecht zu werden, haben viele Organismen innere Uhren entwickelt, welche es ihnen erlauben, den Wechsel von Tag und Nacht vorherzusehen. Diesen inneren Uhren liegt ein molekularer Mechanismus zugrunde, welcher einen Rhythmus von etwa 24 Stunden generiert. Eine wichtige Eigenschaft dieser Uhren ist es, dass sie durch äußere Faktoren, so genannte Zeitgeber, an den Tag-Nacht-Wechsel angepasst werden können. Viele Studien an Mensch, Tier und Pflanze weisen darauf hin, dass Licht der wichtigste Zeitgeber ist, wobei auch Temperatur, Luftfeuchtigkeit oder soziale Interaktionen die innere Uhr an den Tag-Nacht-Wechsel anpassen können. Ziel dieser Arbeit ist es, die Auswirkung von Licht auf das Lauf-verhalten und die innere Uhr genauer zu beleuchten, wozu der Modellorganismus Drosophila melanogaster herangezogen wird. Zahlreiche Forschergruppen haben sich bereits mit der Synchronisation der inneren Uhr durch Licht beschäftigt, wobei klar hervorgeht, dass die Taufliege verschiedene Möglichkeiten hat, Lichtinformationen für die Synchronisation der Uhr zu verwenden. Der wohl am besten untersuchte Prozess ist die Synchronisation durch das Pigment Cryptochrom. Dieses Molekül ist in etwa der Hälfte der Uhrneuronen exprimiert und greift direkt in den molekularen Uhrmechanismus ein, wodurch dieser an den Tag-Nacht-Wechsel angepasst werden kann. Schaltet man jedoch das Gen für dieses Molekül aus so zeigt sich, dass die Tiere dennoch dazu in der Lage sind sich an den Licht-Dunkel-Wechsel anzupassen. Dies bedeutet, dass die visuellen Organe Informationen an die innere Uhr weiterleiten können, wobei der Mechanismus dafür noch nicht vollständig entschlüsselt werden konnte. Selbiges trifft auf sogenannte Maskierungseffekte zu: Maskierung beschreibt eine Veränderung des Verhaltensmusters, welches nicht durch die innere Uhr gesteuert, sondern direkt durch äußere Reize hervorgerufen wird. Diese direkten Effekte komplettieren das Verhalten der Tiere, da sie dadurch selbst zu endogen ungünstigen Zeiten adäquat auf äußere Reize reagieren können. In dieser Arbeit wird sich beider Phänomene angenommen: Zum einen soll die Bedeutung des visuellen Systems für die Synchronisation der inneren Uhr genauer untersucht, und zum anderen soll uhrgesteuertes Verhalten von Maskierung getrennt werden. Zu diesem Zweck wurden Lichtbedingungen simuliert, die den natürlichen ähnelten und die Untersuchung beider lichtabhängiger Effekte ermöglichten. Die Untersuchung von Dämmerung und Mondlicht zeigte deutlich, dass diese starke Veränderungen im Lauf-Verhalten hervorrufen. Die Simulation von Mondlicht bewirkte einen Anstieg der Nachtaktivität und ein Verschieben der Aktivitätsmaxima der Fliege in die Nacht. Das Gegenteil war bei Dämmerungssimulation zu beobachten, da die Tiere mehr Aktivität in den Tag legten. Bei gleichzeitiger Simulation von Mondlicht und Dämmerungsphasen zeigte sich, dass die Dämmerung ein stärkerer Zeitgeber ist als Mondlicht ist. Dieses Ergebnis geht einher mit der Annahme, dass die Dämmerung ein wichtiges Signal für die Synchronisation der inneren Uhr ist, da der Anstieg der Lichtintensität am frühen Morgen unabhängig von der Jahreszeit sehr ähnlich ist. Die Untersuchung von verschiedensten Mutanten konnte zudem zeigen, dass die Komplexaugen der Fliege von größter Bedeutung für die beobachteten Veränderungen im Verhaltensmuster und die Anpassung der inneren Uhr an "natürliche" Lichtbedingungen sind. Dabei stellte sich heraus, dass vor allem die inneren Rezeptorzellen wichtig für die Synchronisation der inneren Uhr und somit uhrgesteuerter Verhaltensänderungen sind. Für Maskierungseffekte scheint eine komplexe Interaktion von mehreren Rezeptorzellen für die Anpassung an Dämmerungs- und Mondlichtbedingungen vorzuliegen, da diese nur bei Mehrfachmutationen verschiedener Rhodopsine, den lichtabsorbierenden Molekülen der Fliege, verschwanden. Jedoch scheinen nicht nur die Komplexaugen das rhythmische Verhalten in Mondlichtnächten zu beeinflussen. Wird das Gen für Cryptochrom, dem Photorezeptor der inneren Uhr, ausgeschaltet, verschieben die Tiere ihre Abendaktivität noch stärker in die Nacht als es bereits beim Wildtyp der Fall ist. Durch verschiedene genetische Manipulationen konnten wir den Grund dieses Verhaltens auf die Expression von Cryptochrom in nur vier Uhrneuronen pro Hemisphäre zurückverfolgen. Zugleich zeigten unsere Ergebnisse, dass die Komplexaugen und Cryptochrom entgegengesetzte Wirkung auf das Timing der Abendaktivität haben. Während die Komplexaugen die Abendaktivität in die Nacht hinein schieben, bewirkt Cryptochrom, dass die Aktivität noch während des Tages stattfindet. Dies bedeutet, dass das wildtypische Verhalten eine Mischung aus beiden Lichteingängen ist und sich die Tiere somit ideal an die äußeren Gegebenheiten anpassen können. Cryptochrom wird jedoch nicht nur in den Uhrneuronen, sondern unter anderem auch in den Komplexaugen der Tiere exprimiert. Um die Funktion in den Augen genauer zu untersuchen, konnten wir in Kollaboration mit Prof. Rodolfo Costa (University of Padova) zunächst zeigen, dass CRY mit der Phototransduktionskaskade über das Protein INAD interagiert und dadurch visuelles Verhalten, wie zum Beispiel Phototaxis oder die optomotorische Antwort, beeinflussen kann. In weiteren Experimenten konnten wir zudem zeigen, dass CRY in den Augen die lokomotorische Aktivität der Fliegen beeinflusst. Dabei trägt es zur Wahrnehmung von Licht bei, ohne jedoch per se ein Photopigment zu sein. Vielmehr scheint CRY die Phototransduktion dahingehend zu verändern, dass es den Phototransduktionskomplex an das Cytoskelett innerhalb der Rhabdomere bindet und somit die Umwandlung von Lichtenergie in elektrische Signale erleichtert. Zusammen mit Prof. Orie Shafer (University of Michigan) ist es uns zudem gelungen, die Rolle des extraretinalen Hofbauer-Buchner-Äugleins für die Synchronisation der Uhr genauer zu beleuchten. Die Anregung des Äugleins führte dabei zu einem Anstieg der Ca2+ und cAMP Mengen in bestimmten Uhrneuronen und dies bewirkte eine Phasenverschiebung des Verhaltens der Taufliege. Somit konnten in dieser Arbeit neue Erkenntnisse über die Funktionen von Cryptochrom und verschiedener Augenstrukturen für das Verhalten der Fliege gewonnen werden. Dabei konnten die Bedeutungen der inneren Uhr sowie von Maskierungseffekten für das Verhalten der Tiere in der Natur herausgearbeitet werden.

G protein coupled receptor (GPCR) kinases (GRKs) phosphorylate activated heptahelical receptors, leading to their uncoupling from G proteins and downregulation. The desensitization of GPCRs is critical to render cells responsive to further stimuli and if not regulated can result in many pathophysiological processes including heart abnormalities and hypertension. How GRKs recognize and are activated by GPCRs are not known, in part because the critical N-terminus and the kinase C-terminal extension were not resolved in GRK2 and GRK6 structures. The long-term goal of this project was to address this question by structural analysis of rhodopsin kinase (also known as GRK1), which represents a model system for studying phosphorylation-dependent desensitization of activated GPCRs. Herein we report structures of GRK1 from six crystal forms that represent three distinct nucleotide-ligand binding states. One of the (Mg²⁺)₂·ADP·GRK1 structures is the most high-resolution structure (1.85 Å) of a GRK to date. In one (Mg²⁺)₂·ATP·GRK1 structure, almost the entire N-terminal region (residues 5-30) is observed. In addition, different segments of the kinase C-terminal extension are ordered in the various nucleotide-bound structures. Together, these two elements form a putative receptor-docking site adjacent to the hinge of the kinase domain. Based on these structures, a model is proposed for how GRK1 interacts with activated rhodopsin and how rhodopsin binding in turn could activate the kinase. Two novel phosphorylation sites were also identified at the N-terminus. The physiological role of phosphorylation sites and the extensive dimerization interface mediated by the regulator of G protein signaling (RGS) homology domain of GRK1 was assessed using site-directed mutagenesis. In addition to mediating interaction with activated GPCRs, the N-terminus of GRKs also forms a binding site for calcium sensing proteins. Although its physiological significance is debated, the structures of these complexes could lend further insights into the conformation of the N-terminus of GRKs. The second chapter deals with attempts to isolate Ca²⁺·recoverin·GRK1 and Ca²⁺·calmodulin·GRK6 complexes. Finally, the RH domain of GRK2 binds G[alpha subscript q], G[alpha]₁₁, and G[alpha]₁₄ subunits thereby blocking their interactions with the downstream effectors. The third chapter involves attempts to isolate a complex of GRK6 and G[alpha]₁₆, a member of G[alpha subscript q] family.

Cellular lipid membranes can – and often do – support a transmembrane electric field, serving as biological capacitors that maintain a voltage difference between their two sides. It isn't hard to see why these voltage gradients matter; the electrical spiking of neurons gives rise to our thoughts and actions, and the voltage dynamics of cardiomyocytes keep our hearts beating. Studies of bioelectricity have historically relied on electrode-based techniques to perturb and measure membrane potential, but these techniques have inherent limitations. I present new optogenetic methods of studying membrane potential that will broaden the scope of electrophysiological investigations by complementing traditional approaches. I introduce the microbial rhodopsin Archaerhodopsin-3 (Arch), a transmembrane protein from Halorubrum sodomense. The fluorescence of Arch is a function of membrane potential, allowing it to serve as an optical voltage reporter. We use time-dependent pump-probe spectroscopy to interrogate the light- and voltage- dependent conformational dynamics of this protein, to elucidate the mechanism of voltage-dependent fluorescence in Arch. I then present two new methods for imaging voltage using engineered variants of Arch. Both techniques take advantage of the unique photophysical properties of Arch(D95X) mutants. The first method, Flash Memory, records a photochemical imprint of the activity state -- firing or not firing -- of a neuron at a user-selected moment in time. The Flash Memory technique decouples the recording of neural activity from its readout, and can potentially allow us to take large-scale snapshots of voltage (e.g. maps of activity in a whole mouse brain). The second method allows for the quantitative optical measurement of membrane potential. This technique overcomes the problems that typically hinder intensity-based measurements by encoding a measurement of voltage in the time domain. Finally, I present a method to visualize cellular responses to changes in membrane potential. I engineer mutants of Channelrhodopsin-2 (ChR2), a light-gated cation channel from Chlamydomonas reinhardtii that is used for optical control of neural activity, and use these optogenetic actuators in conjunction with GFP-based sensors to study the activity-dependent behavior of cultured neurons.

The work described here has focused on two types of supramolecular assemblies, supported lipid bilayers (SLBs) and giant vesicles (GVs) from polymerizable lipids. SLBs are explored extensively as structural models in biophysical studies of cell membranes and biosensor coatings. With regard to implementation as biocompatible scaffoldings for receptor-based molecular devices, fluid SLBs lack chemical, thermal and mechanical stability as lipids are self-organized by weak, noncovalent forces. One possible solution is to use synthetic lipid monomers that can be polymerized to form robust bilayers. A key question is how polymerization affects transmembrane protein structure and activity. Specifically it is unclear if lipid cross-linking can be achieved without adversely affecting the activity of incorporated proteins. In this work the effect of lipid polymerization on transmembrane protein activity was studied with rhodopsin. The protein was reconstituted into SLBs composed of polymerizable lipids, bis-SorbPC, bis-SorbPC:mono-SorbPC, bis-DenPC and bis-SorbPC:mono-SorbPE. Rhodopsin photoactivity was monitored using plasmon waveguide spectroscopy. The results show that reconstitution of rhodopsin into SLBs composed of phosphatidylcholine with the polymerizable moiety in the acyl chain terminus, followed by photoinduced cross-linking of the lipids, does not significantly perturb protein function. A possible explanation is that a bilayer with relatively low Xn retains sufficient elasticity to accommodate the membrane deformation that accompanies the conformational change associated with rhodopsin photoactivation when polymerized in the acyl chain terminus. GVs have diameters ranging from several to few hundred micrometers and thus can be observed by optical microscopic methods. This allows manipulation of individual vesicles and observation of their transformations in real time. GVs have attracted attention as microcontainers for enzymes and drugs, and as biosensors. With the aim of increasing stability for these types of applications, GVs were prepared from synthetic dienoyl lipids that can be polymerized to form robust vesicles. The stability of these vesicles after polymerization was investigated by surfactant treatment, drying and rehydration, and temperature variations. The structure of poly(GVs) was largely retained under these conditions which destroy unpolymerized vesicles. Permeability studies on poly(GVs) suggests that they could be potentially used in a variety of technological applications, including sensors, macromolecular carriers, and microreactors.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 107-117).

Thesis (M.S.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2007. / Includes bibliographical references (p. 117-122).

Frankfurt (Main), University, Diss., 2008.

No description available.

Biochemical and immunological studies indicate that rod outer segments (ROS) of bovine photoreceptor cells contain a Mr 240,000 polypeptide related to the ∝-subunit of red blood cell (RBC) spectrin. With the use of sodium dodecyl sulfate gel electrophoresis in conjunction with the immunoblotting technique, monoclonal antibody 4B2 was found to bind to a Mr 240,000 polypeptide in ROS that is distinct from the prominent Mr 220,000 concanavalin A binding glycoprotein. The Mr 240,000 polypeptide is highly susceptible to degradation by endogenous proteases. It does not appear to be an integral membrane protein but is tightly membrane associated since it can be partially extracted from ROS membranes with urea in the absence of detergent. The 4B2 antibody cross-reacted with RBC ghost membranes and bovine brain microsomal membranes. Radioimmune assays and immunoblotting analysis of purified bovine RBC spectrin further revealed that the 4B2 antibody predominantly labelled the ∝-chain of RBC spectrin having an apparent Mr of 240,000. Monoclonal antibody 3A6 was found to bind to a polypeptide with a slightly lower Mr than the 4B2-specific polypeptide. It is also highly susceptible to degradation by endogenous proteases, but unlike the 4B2 antibody, it predominantly labelled the β-chain of RBC spectrin having an apparent M of 220,000. Polyclonal anti-spectrin antibodies that bound to both the ∝ - and β-chain of RBC spectrin predominantly labelled a Mr 240,000 polypeptide of ROS membranes. Two faintly labelled bands in the Mr range of 210,000-220,000 were also observed. These components may represent variants of the β -chain of spectrin that are weakly cross-reacting or present in smaller quantities than the ∝-chain. Immunocytochemical labelling studies using the 4B2 antibody and immunogold-dextran markers indicated that the ROS spectrin-like protein is preferentially localized in the region where the discs come in close contact to the plasma membrane of ROS. Immunoblotting analysis indicated that rhodopsin and peripherin which constitute over 90% of total disc membrane proteins were selectively solubilized in Triton X-100, whereas a set of polypeptides including the 4B2-specific polypeptide and the Mr 220,000 concanavalin A-binding glycoprotein was only partially soluble. Electron microscopy of a negatively stained Triton-extracted ROS pellet revealed a filamentous network. These studies indicate that ROS contain a protein related to RBC spectrin, which may constitute a major component of a filamentous network lining the inner surface of the ROS plasma membrane as previously seen by electron microscopy. This membrane skeletal system may serve to stabilize the ordered ROS structure and maintain a constant distance between the rim region of the discs and the plasma membrane. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate