In recent years, several interesting biological roles played by RNA have come to light. Apart from their known role in translation of genetic information from DNA to protein, they have been shown to act as enzymes as well as regulators of gene expression. Protein-RNA complexes are involved in regulating cellular processes like cell division, differentiation, growth, cell aging and death. A number of clinically important viruses have RNA as their genetic material. Defective RNA molecules have been linked to a number of human diseases. The ability of RNA to adopt stunningly complex three-dimensional structures aids in diverse functions like catalysis, metabolite sensing and transcriptional control. Several secondary structure motifs are observed in RNA, of which the double-helical RNA motif is ubiquitous and well characterized. Though DNA duplexes have been shown to be present in many polymorphic states, RNA duplexes are believed to exhibit conservatism. Early fibre diffraction analysis on molecular structures of natural and synthetically available oligo- and polynucleotides suggested that the double-helical structures of RNA might exist in two forms: A-form and A′-form. New improved crystallographic methods have contributed to the increased availability of atomic resolution structures of many biologically significant RNA molecules. With the available structural information, it is feasible to try and understand the contribution of the variations at the base pair, base-pair step and backbone torsion angle level to the overall structure of the RNA duplex. Further, the effect of protein binding on RNA structure has not been extensively analysed. These studies have not been investigated in greater detail due to the focus of the research community on understanding conformational changes in proteins when bound to RNA, and due to the lack of a significant number of solved RNA structures in both free and protein-bound state. While studies on the conformation of the DNA double-helical stem have moved beyond the dinucleotide step into tri-, tetra-, hexa- and octanucleotide levels, similar knowledge for RNA even at the dinucleotide step level is lacking. In this thesis, the results of detailed analyses to understand the contribution of the base sequence towards RNA conformational variability as well as the structural changes incurred upon protein binding are reported. Objectives The primary objective of this thesis is to understand the following through detailed analyses of all available high-resolution crystal structures of RNA. 1 Exploring sequence-dependent variations exhibited by dinucleotide steps formed by Watson-Crick (WC) base pairs in RNA duplexes. 2 Identifying sequence-dependent variations exhibited by dinucleotide steps containing non-Watson-Crick (NWC) base pairs in RNA duplexes. 3 Developing a web application for the generation of sequence-dependent non-uniform nucleic acid structures. 4 Investigating the relationship between base sequence and backbone torsion-angle preferences in RNA double helices followed by molecular dynamics simulation using various force fields, to check their ability to reproduce the above experimental findings. Chapter 1 gives an overview of the structural features and polymorphic states of RNA duplexes and the present understanding of the structural architecture of RNA, thereby laying the background to the studies carried out subsequently. The chapter also gives a brief description on the methodologies applied. Relevant methodologies and protocols are dealt with in detail in the respective chapters. Sequence-dependent base-pair step geometries in RNA duplexes A complete understanding of the conformational variability seen in duplex RNA molecules at the dinucleotide step level can aid in the understanding of their function. This work was carried out to derive geometric information using a non-redundant RNA crystal structure dataset and to understand the conformational features (base pair and base-pair step parameters) involving all Watson-Crick (WC) (Chapter 2) and non-Watson-Crick (NWC) base pairs (Chapter 3). The sequence-dependent variations exhibited by the base-pair steps in RNA duplexes are elaborated. Further, potential non-canonical hydrogen bond interactions in the steps are identified and their relationship with dinucleotide step geometry is discussed. Comparison of the features of dinucleotide steps between free and protein-bound RNA datasets suggest variations at the base-pair step level on protein binding, which are more pronounced in non-Watson-Crick base pair containing steps. Chapter 4 describes a web-server NUCGEN-Plus, developed for building and regeneration of curved and non-uniform DNA and RNA duplexes. The main algorithm is a modification of our earlier program NUCGEN that worked mainly for DNA. The WC step parameters and intra-base parameters for RNA were obtained from the work detailed in Chapter 2. The FORTRAN code and input sequence file format was modified. The program has two modules: a) Using the model-building module, the program can build duplex structures for a given input DNA/RNA sequence. Options are available for selecting various derived or user specified base-pair step parameters, and fibre diffraction parameters that can be used in the building process. The program can generate double-helical structures up to 2000 nucleotides in length. In addition, the program can calculate the curvature of the generated duplex at defined length scale. b) Using the regeneration module, double-helical structures of nucleic acids can be rebuilt from the existing solved structures. Further, variants of an existing structure can be generated by varying the input geometric parameters. The web-server has a user-friendly interface and is freely available in the public domain at: http://nucleix.mbu.iisc.ernet.in/nucgenplus/index.html Sequence dependence of backbone torsion angle conformers in RNA duplexes RNA molecules consist of covalently linked nucleotide units. Each of these units has six rigid torsional degrees of freedom (α, β, γ, δ, ε, and ζ) for the backbone and one (χ) around the glycosidic bond connecting the base to the ribose, thereby providing conformational flexibility. An understanding of the relationship between base sequence and structural variations along the backbone can help deduce the rationale for sequence conservation and also their functional importance. Chapter 5 describes in detail the torsion angle-dependent variations seen in dinucleotide steps of RNA duplex. A non-redundant, high resolution (≤2.5Å) crystal structure dataset was created. Base-specific preferences for the backbone and glycosidic torsion angles were observed. Non-A-form torsion angle conformers were found to have a greater prevalence in protein-bound duplexes. Further validation of the above observation was performed by analysing the RNA backbone conformers and the effect of protein binding, in the crystal structure of E. coli 70S ribosome. Chapter 5 further describes the molecular dynamics simulation studies carried out to understand the effect of force fields on the RNA backbone conformer preferences. A 33mer long duplex was simulated using seven different force fields available in AMBER and CHARMM program, each for 100 ns. Trajectory analyses suggest the presence of sequence-dependent torsion angle preferences. Torsion angle conformer distribution closer to that of crystal structures was observed in the system simulated using parmbsc0 force field. Molecular dynamics simulation studies of AU/AU base-pair step A unique geometric feature, unlike that in other purine-pyrimidine (RY) steps in the crystal dataset analysis, was reported for AU/AU step (see Chapter 2). Appendix 1 describes the work carried out to validate these features observed in the crystal structures using simulation studies. Additionally, the effect of nearest-neighbor base pairs on the AU/AU step geometry were examined. General Conclusion Overall, the findings of this thesis work suggest that RNA duplexes exhibit sequence-dependent structural variations and sample a large volume of the double-helical conformational space. Further, protein binding affects the local base-pair step geometry and backbone conformation.

Photonic bandgap structures have provided promising platform for miniaturization of modern integrated optical devices. In this thesis, a photonic crystal based ring resonator (PCRR) is proposed and optimized to exhibit high quality factor. Also, force sensing application of the optimized PC ring resonator and Dense Wavelength Division Multiplexing (DWDM) application of the PCRR are discussed. Finally fabrication and characterization of the PCRR is presented. A photonic crystal ring resonator is designed in a hexagonal lattice of air holes on a silicon slab. A novel approach is used to optimize PCRR to achieve high quality factor. The numerical analysis of the optimized photonic crystal ring resonator is presented in detail. For all electromagnetic computations Finite Difference Time Domain (FDTD) method is used. The improvement in Q factor is explained by using the physical phenomenon, multipole cancellation of the radiation held of the PCRR cavity. The corresponding mathematical frame work has been included. The forced cancellation of lower order radiation components are verified by plotting far held radiation pattern of the PCRR cavity. Then, the force sensing application of the optimized PCRR is presented. A high sensitive force sensor based on photonic crystal ring resonator integrated with silicon micro cantilever is presented. The design and modelling of the device, including the mechanics of the cantilever, FEM (Finite Element Method) analysis of the cantilever beam with PC and without PC integrated on it. The force sensing characteristics are presented for forces in the range of 0 to 1 N. For forces which are in the range of few tens of N, a force sensor with bilayer cantilever is considered. PC ring resonator on the bilayer of 220nm thick silicon and 600nm thick SiO2 plays the role of sensing element. Force sensing characteristics of the bilayer cantilever for forces in the range of 0 to 10 N are presented. Fabrication and characterization of PCRR is also carried out. This experimental work is done mainly to understand practical issues in study of photonic crystal ring resonators. It is proved that Q factor of PCRR can be signi cantly improved by varying the PCRR parameters by the proposed method. Dense Wavelength Division Multiplexing (DWDM) application of PC ring resonator is included. A novel 4-channel PC based demultiplexer is proposed and optimized in order to tolerate the fabrication errors and exhibit optimal cross talk, coupling efficiency between resonator and various channels of the device. Since the intention of this design is, to achieve the device performance that is independent of the unavoidable fabrication errors, the tolerance studies are made on the performance of the device towards the fabrication errors in the dimension of various related parameters. In conclusion we summarize major results, applications including computations and practical measurements of this work and suggest future work that may be carried out later.

Les glutathion transférases (GSTs) constituent une superfamille ubiquitaire d’enzymes multifonctionnelles impliquées dans les processus de détoxication cellulaire en métabolisant des substrats exogènes appelés xénobiotiques et dans le métabolisme secondaire. Pour cela, ces enzymes peuvent catalyser la conjugaison d’une molécule de glutathion (GSH) sur les composés ciblés ou simplement les lier au travers d’une fonction ligandine. Alors que la fonction de conjugaison est catalysée par les GSTs possédant une sérine ou une tyrosine comme résidu catalytique, certaines d’entre elles possèdent à la place une cystéine. Cette substitution change radicalement leurs propriétés puisque les GSTs à cystéine (Cys-GSTs) catalysent plutôt des réactions de déglutathionylation. Les Cys-GSTs sont retrouvées chez la plupart des organismes et sont réparties en plusieurs classes. Chez les plantes, on trouve principalement 4 classes : déshydroascorbate réductases (DHARs), GSTs Lambda (GSTLs), glutathionyl hydroquinone réductases (GHRs) et mPGES2 (microsomal prostaglandine E-synthase type 2). Alors que le rôle des DHARs semble clairement associé à la réduction du déshydroascorbate en ascorbate, la fonction physiologique des autres Cys-GSTs reste majoritairement inconnue. En combinant des approches moléculaires, cellulaires, biochimiques et structurales, l’analyse fonctionnelle des deux GHRs, des trois GSTLs et des trois DHARs chez l’arbre modèle Populus trichocarpa a été entreprise. De façon intéressante, les gènes GSTL et GHR sont majoritairement exprimés dans les fleurs, les fruits et les pétioles par rapport aux feuilles et aux racines. A l’inverse, les gènes DHAR sont principalement exprimés dans les feuilles. De plus, l’expression transitoire de protéines fusionnées à la GFP dans le tabac a montré que les GSTLs et les DHARs sont localisées dans les plastes, le cytoplasme et le noyau alors que les GHRs sont toutes plastidiales. Les études biochimiques et structurales effectuées à l’aide des protéines recombinantes et de substrats modèles ont montré que la plupart des Cys-GSTs possèdent des activités et des structures assez semblables. Cependant, bien que les GSTLs et les DHARs adoptent un repliement GST canonique classique proche de celui des GSTs Oméga fongiques et humaines, elles sont monomériques alors que les GSTs Oméga sont dimériques. Les GHRs sont particulières tant au niveau de leur interface de dimérisation unique qu’au niveau de leurs propriétés spécifiques de réduction de quinones glutathionylées. En résumé, la nature des substrats fixés par les Cys-GSTs (composés cycliques aromatiques) ainsi que les territoires d’expression de ces gènes et protéines suggèrent que ces protéines sont globalement impliquées dans la protection des plantes face aux contraintes environnementales via la modification, le stockage et/ou le transport de métabolites secondaires et autres composés antioxydants. Toutefois, l’objectif suivant sera de déterminer la nature exacte des substrats/ligands associés à chaque enzyme / Glutathione transferases (GSTs) constitute a ubiquitous superfamily of multifunctional enzymes involved in cellular detoxification processes by metabolizing exogenous substrates called xenobiotics and in secondary metabolism. For this purpose, these enzymes catalyze the conjugation of a glutathione molecule (GSH) onto target compounds or simply bind them through a ligandin function. While conjugation reactions are catalyzed by GSTs having a serine or a tyrosine as catalytic residues, other GSTs possess a cysteine. This substitution radically changes their properties since GSTs having a cysteine (Cys-GSTs) rather catalyze deglutathionylation reactions. Cys-GSTs are found in most organisms and are divided into several classes. In plants, there are mainly four classes: dehydroascorbate reductases (DHARs), Lambda GSTs (GSTLs), glutathionyl hydroquinone reductases (GHRs), and microsomal prostaglandin E-synthase type 2 (mPGES). While the role of DHARs seems clearly associated to the reduction of dehydroascorbate into ascorbate, the physiological function of other Cys-GSTs remains largely unknown. By combining molecular, cellular, biochemical and structural approaches, the functional analysis of the two GHRs, the three GSTLs and the three DHARs in the model tree Populus trichocarpa was undertaken. Interestingly, GSTL and GHR genes are predominantly expressed in flowers, fruits and petioles compared to leaves and roots. Conversely, the DHAR genes are mainly expressed in leaves. Furthermore, transient expression of proteins fused to GFP in tobacco showed that GSTLs and DHARs are localized in plastids, cytoplasm and nucleus while GHRs are all localized in plastids. Biochemical and structural studies using recombinant proteins and model substrates showed that most Cys-GSTs have similar activities and structures. However, although GSTLs and DHARs adopt a canonical GST folding similar to that of fungal and human Omega GSTs, they are monomeric whereas Omega GSTs are dimeric. GHRs are particular owing to their unique dimerization interface and to their specific capacity to reduce glutathionylated quinones. In summary, the nature of the substrates bound by Cys-GSTs (heterocyclic aromatic compounds) as well as the expression territories of these genes and proteins, suggest that they are generally involved in the protection of plants towards environmental constraints through the modification, storage and/or transport of secondary metabolites and other antioxidants. However, the next goal will be to determine the exact nature of the substrates/ligands associated with each enzyme

A flexible Metal–Organic Framework Zn4O(BenzTB)3/2 (DUT-13) was obtained by combination of a tetratopic linker and Zn4O6+ as connector. The material has a corundum topology and shows the highest pore volume among flexible MOFs. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Transition-metal chemistry in ionic liquids (IL) has achieved intrinsic fascination in the last few years. The use of an IL as environmental friendly solvent, offers many advantages over traditional materials synthesis methods. The change from molecular to ionic reaction media leads to new types of materials being accessible. Room-temperature IL have been found to be excellent media for stabilising transition-metal clusters in solution and to crystallise homo- and heteronuclear transition-metal complexes and clusters. Furthermore, the use of IL as solvent provides the option to replace high-temperature routes, such as crystallisation from the melt or gas-phase deposition, by convenient room- or low-temperature syntheses. Inorganic IL composed of alkali metal cations and polynuclear transition-metal cluster anions are also known. Each of these areas will be discussed briefly in this contribution. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Ionic liquids (ILs) have made a great impact on materials science and are being explored for potential applications in several disciplines. In this article, we briefly highlight the current state-of-the-art techniques employing ILs as new crystallisation media, working as neutral solvent, template or charge compensating species. The use of an IL as environmental friendly solvent offers many advantages over traditional crystallisation methods. The change from molecular to ionic reaction media leads to new types of materials being accessible. Room temperature ILs have been found to be excellent solvent systems for the crystallisation of a wide range of substances and morphologies ranging from nanoscopic crystals to micro- and even to macroscopic crystals. Moreover, high temperature routes, such as crystallisation from melts or gas phase deposition, have been replaced by convenient room or low temperature syntheses, employing ILs as reaction media. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Self-assembly processes were used to construct supramolecular architectures based on metal-ligand interactions. The structures formed strongly depend on the used metal ion, the ligand type, the chosen counter ion and solvent as well as on the experimental conditions. The focus of the studies was the design of multifunctional N-donor ligands and the characterization of their complexing and structural properties. This work was divided into three distinct main parts: The bis(2-pyridylimine), the bis(2-hydroxyaryl) imine and the tripodal imine / amine ligand approach. In the first part a series of bis(2-pyridylimine) derivatives having different linking elements were employed as building blocks for novel supramolecular architectures. Reaction of individual d-block metal salts with these ligands has led to the isolation of coordination polymers, a metallamacrocycle, double-stranded helicates, triple-stranded helicates as well as of circular meso-helicates. The nature of the spacer in the Schiff base ligands, the noncovalent weak interactions, such as hydrogen bond, face-to-face π-π and edge-to-face CH-π interactions, are all important factors influencing the architecture of the final products. Topological control of the assembly process of the hexanuclear meso-helicates is clearly associated with the bidentate coordination of the sulfate anion which directs the formation of a double- rather than a triple-stranded helicate around the octahedrally coordinated Cu(II). Surprisingly, the variation of the linker function in the ligands, which significantly changes the linking angle of the pyridylimine strands, has only a little influence of the resulting structure. Also the use of a mixture of ligands does not influence the meso-helicate topology; the result is the symmetrically mixed meso-helicate. The new iron(II) triple helicate [Fe2(L5)3](PF6)4 14 {L5 = bis[4-(2-pyridylmethyleneimino)phenyl]-1,1-cyclohexane} in its chloride form binds strongly to DNA as confirmed by induced circular dichroism signals in both the metal-to-ligand charge transfer (MLCT) and in-ligand bands of the helicate. The induced CD spectrum gives some evidence that [Fe2(L5)3]4+ interacts with the DNA in a single binding mode, which is consistent with major groove binding. The cytotoxicity of the new iron(II) triple helicate 14 was evaluated on human lung cancer A549 cells and compared with that of cisplatin and that of the previously reported iron(II) triple helicate [Fe2(L1)3]4+{L1 = bis[4-(2-pyridylmethyleneimino)phenyl]methane}. The first results show some distinguishing features for 14 obviously caused by the existing structural differences of the complexes. In the second part of the thesis, novel uranyl complexes of the bis(2-hydroxyaryl) imine ligands have been synthesized and characterized. 1D coordination polymers and mononuclear structures were formed. In all complexes a distorted hexagonal bipyramidal coordination geometry around the uranyl centre is observed. The imine nitrogen atoms of the ligands do not bind to the metal centre but interact strongly with the hydroxy group via H-bonding. DFT calculations made with L8 ( α,α’-Bis(salicylimino)-m-xylene) are in good agreement with the X-ray crystal structure data. Liquid-liquid extraction studies involving selected ligands and Eu(III) or U(VI) indicate remarkably high selectivity for U(VI) over Eu(III) at weak acidic pH conditions. We believe that the study made opens up new possibilities for uranyl ion extraction which could be interesting in view of the treatment of nuclear waste. In the third part of the thesis, a series of multifunctional tripodal ligands with different N-donor centres were used for U(VI) and lanthanide, Nd(III), Eu(III) and Yb(III), binding and extraction. Reaction of these metal ions with selected tripodal ligands afforded complexes which were characterized by ESI mass spectroscopy. The complex composition was found to be 1:1 in all cases. The extraction behaviour of the tripodal ligands towards Eu(III) and U(VI) was studied both in the absence and presence of octanoic acid as co-ligand using the extraction system Eu(NO3)3 or UO2(NO3)2–buffer–H2O/ ligand–CHCl3. These separation systems show a remarkably high selectivity for U(VI) over Eu(III). It is interesting to note that the addition of the octanoic acid to the extraction system leads to high synergistic effects. A series of Eu(III) extraction experiments were done to clarify the composition of the extracted complexes. The results clearly point to the formation of various species with changing composition.

Systematic synthetic investigations of the quaternary systems Ag - Bi - Q - X (Q = S, Se; X = Cl, Br) led to a variety of quaternary phases that exhibit considerable structural diversity with increasing complexity. These include Ag1.2Bi17.6S23Cl8, AgBi4Se5Br3 and numerous members of the homologous double series Agx(N+1)Bi2+(1-x)(N+1)Q2+(2-2x)(N+1)X2+(2x-1)(N+1) denoted (N, x)P. N represents the order number of a given homologue and x is the degree of substitution of Bi by Ag with 1/2 <= x <= 1. Their structures are built up from two alternating types of modules denoted A and B that are stacked parallel to (001). In module A, rows of edge-sharing [MZ6] octahedra (Z = X and/or Q); M = Ag and/or Bi) running parallel to [010] alternate along [100] with parallel chains of paired monocapped trigonal prisms around Bi atoms. The module type denoted B represents NaCl-type fragments of varying thickness. It is defined by the number N of octahedra within the chain of edge-sharing octahedra running diagonally across it in the (010) plane of the structure. The thickness of module B for current members of the series extends from N = 0 to N = 7. All structures exhibit Ag/Bi disorder in octahedrally coordinated metal positions and Q/X (Q = S, Se; X = Cl, Br) mixed occupation of some anion positions. Some of these compounds are narrow gap semiconductors.

This thesis describes the syntheses, the crystal structures, and the physical properties of some new ternary and quaternary rare-earth coinage metal arsenides, selenides and oxides. All ternary compounds LnCu1+[delta]As2 (Ln = Y, La, Ce, Nd, Sm, Gd - Lu), LnAg1+[delta]As2 (Ln = La - Nd, Sm), and LnAuAs2 (Ln = Pr, Sm, Gd, Tb) adopt structures closely related to the HfCuSi2 type consisting of PbO-like layers of T and As atoms, square layers of As atoms and layers of Ln atoms separating the former two building units. All copper compounds of this series contain regular square nets of As atoms, whereas the respective nets in the silver and gold compounds are distorted. Two principally different patterns of distortion have been found: [As] zigzag chains in LnAgAs2 (Ln = Pr, Nd, Sm) and [As] cis-trans chains in LaAg1.01(1)As2, CeAgAs2, and PrAuAs2. Both patterns can undergo a further reduction of symmetry to end up with a pattern of As2 dumb-bells as can be seen in SmAuAs2, GdAuAs2, and TbAuAs2. Stoichiometric samples LnCuAs2 (Ln = Y, Pr, Nd, Sm, Gd, Tb, Dy, Er) have been used for measurements of the conductivity [rho], magnetic susceptibility [chi] and heat capacity cp. All investigated compounds exhibit metallic conductivity and, except for Y, order antiferromagnetically at temperatures below 10 K. In contrast to LnCuAs2 compounds, the silver compound CeAgAs2 shows semiconducting behavior throughout the temperature range from 4 to 350 K, whereas in PrAgAs2 metallic conductivity is preserved. The crystal structure of Sm2CuAs3O contains two different PbO-like layers formed either by Sm and O or Cu and As atoms. Both PbO-type layers are separated by sheets of Sm and distorted square nets of As atoms. The As atoms are arranged in planar zigzag chains, like those found in NdAgAs2. Sm2CuAs3O is thus the first quaternary rare-earth pnictide oxide with a distorted As net. The quaternary potassium rare-earth copper selenides KGd2CuSe4, KLn2Cu3Se5 (Ln = Ho, Er, Tm), and K2Ln4Cu4Se9 (Ln = Dy, Y) extend three series of previously described sulfide and selenide compounds. All three series adopt a three-dimensional tunnel structure built up by [LnSe6] octahedra and [CuSe4] tetrahedra. The K atoms reside in the tunnels with a bicapped trigonal prismatic coordination of eight Se atoms for KGd2CuSe4 and KLn2Cu3Se5 (Ln = Ho, Er, Tm), while for K2Ln4Cu4Se9 (Ln = Dy, Y), the K atoms are coordinated by seven Se atoms in monocappped trigonal prisms.

<p> We developed some universal platforms to overexpress the minimal functional entities of ion channels. The modular property of ion channels have been demonstrated from many aspects, such as crystal structures, chimeric channel experiments and discovery of similar modules in distantly related protein families. Thus it should be feasible to express each module independent of other channel modules. The pore-forming module of ion channels has multiple important properties as selectivity, conductivity and drug-binding. If it can be overexpressed, it will provide valuable information about channel selectivity to different ions and structural bases for drug binding as well as important application in drug screening and rational drug design. </p> <p> To test this, we first used the model channel KcsA to identify the minimal requirements for a pore-forming domain to functionally exist independently. Chapter 2 of this thesis explains in detail how the wild type C-terminal cytoplasmic domain of KcsA functions. We found that this domain has dual function as pH-sensor and tetramerization domain, and it is essential for the expression of the pore-forming domain of KcsA. Once we knew the physiological role of the cytoplasmic domain, the scenario was set to answer the question of how to make it better for the application of structural and functional studies. </p> <p> In chapter 3 and chapter 4, we replaced the wild type C-terminal domain with non-native tetramerization domains. We identified the direct correlation between protein expression level and overall thermostability of pore-forming domains. The C-terminal tetramerization domains stabilize channels in a cooperative way and play a critical way in in vivo channel assembly. The selection of the linker between pore-forming domain and tetramerization domain, the splicing motif, and the handedness of C-terminal tetrameric coiled coils all affect channel expression level and stability. </p> <p> We applied our finding in KcsA to a wide range of ion channels in chapter 5, including voltage-gated potassium channels, Ca2+-gated potassium channels, inwardrectifying potassium channels, cyclic nucleotide-gated potassium channels and voltagegated sodium channels. We managed to express similar minimal structural modules from these more structurally complicated channels with the assistance of different cytoplasmic tetramerization domains. Several minimal channels expressed well and showed similar biophysical and functional property as the wild type channels. </p> <p> These studies demonstrate that the pore-forming modules of ion channels can be expressed independently while retaining the proper structure and drug-binding properties as their wild type predecessors when using our universal expression platform. The potential application in structural studies and drug-screening is promising. </p> / Thesis / Doctor of Philosophy (PhD)