Crystal structures of Aldose Reductase, C2A domain of Rabphilin3A and tests of new restraints.

In dieser Arbeit wird die hochaufgelöste (0.82 Å) Struktur der Aldose-Reduktase (ein Enzym, welches am polyol Stoffwechselweg beteiligt ist) vorgestellt. Das Ziel der Arbeit war eine sorgfältige Überprüfung des Modells mit Schwerpunkt auf Merkmale, die nur bei hoher Auflösung erkennbar sind. Daten von atomarer Auflösung erlaubten die Modellierung mehrerer verschiedener Konformationen als in früher bestimmten Strukturen, sowie eine Verbesserung der Übereinstimmung von Modell und Daten. Besondere Aufmerksamkeit wurde der Liste der disagreeable restraints gewidmet: einige kamen wahrscheinlich durch falsche restraints zustande, während andere reale Merkmale der Struktur sind, die nur bei hoher Auflösung sichtbar werden. Diese Beobachtungen könnten verwendet werden, um sowohl eine neue restraints library zu erstellen, als auch um die Molekülstruktur und funktion im Detail zu erklären. Das interessanteste Merkmal des Modells ist die Sicherheitsgurtschleife , die in zwei eigenständigen Konformationen sichtbar ist, der allgemeinen geschlossenen und einer zum Teil geöffneten Konformation (welche möglich ist, weil sich das Enzym in ein post-reaktivem Zustand befindet). Die Aufhebung einer Wechselwirkung genügt, um die Freisetzung des Kofaktors zu bewirken und die Sicherheitsgurtschleife zu öffnen. Die sorgfältige Untersuchung verschiedener hochaufgelöster Aldose-Reduktase Strukturen ergab eine Domänenbewegung die "Zangenbewegung" genannt wurde: die oberen und unteren Schleifen nähern sich dabei an oder entfernen sich voneinander, während das β-barrel starr bleibt. Diese Bewegung könnte mit dem post-reaktiven Zustand des Enzyms und der Freisetzung des Kofaktors zusammenhängen.Weiterhin wird die Kristallstruktur der Ca2+-freien C2A-Domäne von Rabphilin3A (einem neuronalen Protein, das am synaptischen Vesikelzyklus beteiligt ist und dessen genaue biologische Funktion noch ungeklärt ist) bei einer Auflösung von 1.92 Å vorgestellt. Die Struktur besitzt eine Typ1-Topologie und ist durch ein achtsträngiges antiparalleles β-Sandwich charakerisiert. Die elektrostatische Oberfläche ist sehr basisch und weist große Ähnlichkeiten zur C2B-Domäne des Rabphilin3A auf. In der C2A-Domäne des Rabphilin3A wurden zwei strukturelle Merkmale, die durch Unterschiede zur Konsensussequenz zustande kommen, gefunden: eine abweichende Position der Kalziumbindungsschleife 1 (CBL1), wodurch eine deutliche räumliche Verlagerung des konservierten, an der Ca2+-Bindung beteiligten Restes Asp413 verursacht wird, und die Anwesenheit des Restes Glu475 (im DED-Motiv), durch welchen eine lokale negative Ladung nahe der Ca2+-Bindungstelle entsteht. Im Vergleich zu anderen C2 Domänen weist die Struktur andere Merkmale auf, was ein Hinweis auf eine neue Funktion dieser Domäne sein könnte.Im letzten Kapitel werden Überprüfungen mittels einer neuen SHELXL Version, in der ein restraint an ADP gelegt wurde, gezeigt. Der neue restraint imitiert eine TLS Verfeinerung und sollte für Daten mittlerer Auflösung (1.5 - 2.0 Å) nützlich sein. Es wurden Vergleiche zwischen Strukturen, welche sowohl mit TLS in REFMAC als auch mit zwei SHELXL Versionen bei verschiedenen Auflösungen verfeinert wurden, angestellt. Die Ergebnisse zeigen, dass die beiden Programme bei mittlerer Auflösung vergleichbare Daten liefen. Der neue restraint ist allerdings eine gute Verbesserung im Vergleich zu der alten SHELXL Version

Analisi di un convertitore ad elevato guadagno di tensione con topologia Boost Interleaved risonante

Questo documento descrive l'analisi steady state del convertitore IBCI (Interleaved Boost with Coupled Inductors) in funzionamento risonante. Ci si prefigge di determinare le relazioni che intercorrono tra il rapporto di conversione e i segnali di controllo quali duty cycle, frequenza di switching e risonanza. Il funzionamento risonante garantisce da un lato un maggior guadagno in tensione del convertitore e dall'altro la possibilità di controllare ulteriori aspetti, quali le perditeope

Identification of a novel polyfluorinated compound as a lead to inhibit human enzymes aldose reductase and AKR1B10 : structure determination of both ternary complexes and implications for drug design

Aldo-keto reductases (AKRs) are mostly monomeric enzymes which fold into a highly conserved ([alpha]/[beta])8 barrel, while their substrate specificity and inhibitor selectivity are determined by interaction with residues located in three highly variable external loops. The closely related human enzymes aldose reductase (AR or AKR1B1) and AKR1B10 are of biomedical interest because of their involvement in secondary diabetic complications (AR) and in cancer, e.g. hepatocellular carcinoma and smoking-related lung cancer (AKR1B10). After characterization of the IC50 values of both AKRs with a series of polyhalogenated compounds, 2,2',3,3',5,5',6,6'-octafluoro-4,4'-biphenyldiol (JF0064) was identified as a lead inhibitor of both enzymes with a new scaffold (a 1,1'-biphenyl-4,4'-diol). An ultrahigh-resolution X-ray structure of the AR-­NADP+-JF0064 complex has been determined at 0.85 Å resolution, allowing it to be observed that JF0064 interacts with the catalytic residue Tyr48 through a negatively charged hydroxyl group (i.e. the acidic phenol). The non-competitive inhibition pattern observed for JF0064 with both enzymes suggests that this acidic hydroxyl group is also present in the case of AKR1B10. Moreover, the combination of surface lysine methylation and the introduction of K125R and V301L mutations enabled the determination of the X-ray crystallo­graphic structure of the corresponding AKR1B10-NADP+-JF0064 complex. Comparison of the two structures has unveiled some important hints for subsequent structure-based drug-design efforts

High Efficiency Interfacing Converters for Distributed Energy Systems

The ever-growing amount of renewable energy sources connected to the grid call for a revision of the traditional concept of energy distribution network. In addition, the world climate change issue is becoming a major task for the green energy technology development in the last decades. In the last years, the smart grids are the promising paradigm shift for the low- and medium-voltage grids. The term smart grid indicates the symbiosis of the traditional distribution network with a deeply branched ICT infrastructure. The fundamental benefits of this cooperation is an increase in efficiency, reliability and stability of the whole electrical system, and a minimization of the costs and environmental impacts. The main differences with respect to the traditional distribution grid are the growing arrays of customer-sited distributed energy resources (DERs), including renewable energy sources and storage systems, instead of the large and centralized power plants present in the tra- ditional grid. To control and monitor the overall grid system, the ICT infrastructure must be able to manage the present agents, i.e. DERs, and the latter need to be interfaced with the distribution network through Electronic Power Converters (EPCs) forming a micro-, nano-, pico-grid according to the geographical extension. A typical example of pico-grid is a smart building: renewable energy sources, e.g. photovoltaic (PV) panel or wind generator, and energy storage systems, e.g. battery and/or supercapacitor, are connected together through a common DC Link bus. The interface between DERs and DC Link is demanded to EPCs that manage the power flow, optimize the source utilization or the time-profile generation via the energy storage. The power transfer, besides taking place among the connected DERs, can occur between the DC link and the grid through an AC/DC converter (inverter). The main aim of the presented work is to look into the EPC design procedure to achieve a deep integration of DERs in the future smart grid. To this end, the efficiency and the power density are considered the main performance indices to achieve a more effective EPC design. Since the design process involves the optimization of many performance indices, the first part of this work is dedicated to a general overview of Multi-Objective Optimization problem is discussed to provide the sufficient theoretical background to handle with new methodology. Initially, an example of application of MOO is presented to introduce the notation and show the methodology in a simple case, then the EPC optimization is included. The central part of the dissertation focuses on the needed background to allow a proper converters modelling. The considered objectives, i.e. efficiency and power density of the considered EPC, are related to the losses, that occurs during the power transfer in the EPC, and the final volume of the converter. Because of this, the estimation of the losses and volume for each electronic components of EPC becomes mandatory. However, the choice of the accuracy of the models used to predict losses and volume is a degree of freedom, since it greatly impacts on computational time. Since this approach is considered in this dissertation a first valuation to make comparison between innovative solutions and the state of the art, the models consider only the main contribution of each loss phenomenon and the main volume contributions. In this way, the MOO analysis doesn’t become a high time- and data-consumption tool. The series resonant converters will be treated in detail because of their many advantages: inherent short circuit protection, higher operation frequency, lower electromagnetic interferences and soft-switching modulation. An innovative mathematical framework is proposed for their steady-state analysis, providing the closed-form solutions of the sampled resonant impedance state, the voltage conversion ratio and the transferred power in a single matrix formulation. This tool has been validated by means of a high efficiency DC/DC topology for renewable source interfacing: the Interleaved Boost with Coupled Inductors (IBCI). The proposed framework has allowed to identify six different operating modes providing the closed-form expressions of the voltage conversion ratios and the operating boundaries. Furthermore, the sampled state variable trajectories lays out some soft switching considerations. The testcase demonstrates the effectiveness of the proposed method also with complex topologies avoiding simulation-based or approximated analysis. In the latter part of the work, the input stage of an AC/DC converter is presented to validate the usage of the MOO approach: the Power Factor Correction (PFC) Boost stage design in a Medium Voltage Solid State Transformer . The analysis is carried out to obtain the concrete benefits introduced by the implementation of a proposed solution to reduce the losses in the switches

Analisi di un convertitore ad elevato guadagno di tensione con topologia Boost Interleaved risonante

Questo documento descrive l'analisi steady state del convertitore IBCI (Interleaved Boost with Coupled Inductors) in funzionamento risonante. Ci si prefigge di determinare le relazioni che intercorrono tra il rapporto di conversione e i segnali di controllo quali duty cycle, frequenza di switching e risonanza. Il funzionamento risonante garantisce da un lato un maggior guadagno in tensione del convertitore e dall'altro la possibilità di controllare ulteriori aspetti, quali le perdit

Spectrum Estimation of Input Current Ripple on a Wide Class of Multilevel Grid-Tied Converters

Multilevel (ML) converters are frequently used to implement grid-tied ac-dc conversion systems. Their design may benefit from multiobjective optimization techniques, which typically involves time-consuming circuit simulations in order to obtain input current estimations suitable for input inductor and electromagnetic interference filter design. Herein, a closed-form expression of the input current ripple is derived to ease harmonic content estimations. The proposed approach separates the fundamental grid-current component from its ripple and models the latter like an amplitude modulation, where the modulating signal is its envelope and the carrier is the triangular current waveform. First, a general waveform analysis of ML converters is performed to derive the voltage across the grid-side inductor, then the associated current ripple is modeled. Experimental results on an ML converter prototype are reported to validate the analytical results