Gene regulation is vital to the success of all living organisms. Understanding this complex process is crucial to our knowledge of how cells function and how in some cases they can lead to debilitating or even fatal disease. In this thesis I focus on a set of DNA-binding proteins known as transcription factors (TFs), proteins fundamental to the process of gene regulation at the level of transcription. I develop assays and techniques for the detection and quantitation of TFs in vitro and in vivo as well as a method for TF encapsulation and release. The advantages of the TF detection assays in this thesis are made possible through the use of single-molecule (sm) fluorescence. This methodology enables detection of individually labeled molecules allowing discrimination of sample heterogeneities inaccessible with ensemble techniques. Here I present two different TF assays based on two sm observables: relative probe stoichiometry and Förster resonance energy transfer (FRET). The first assay design, based on stoichiometry, detects TFs using TF-dependent coincidence of two distinctly labelled DNA ‘half-sites’. I demonstrate sensitive detection (~ pM) in solution and on surfaces, multiplexed detection of multiple TFs, and detection in cell lysates. A kinetic model of the system is also developed, verified experimentally and used to quantify TF concentrations without the need for a calibration curve. The second assay design, based on FRET, is a novel approach to TF detection using TFmediated DNA bending. TFs are detected by bending the sensor and monitored with FRET at the single-molecule or ensemble level. I demonstrate TF detection in purifed form and expressed in cell lysates. As this sensor was designed for use in vivo, methods to hinder nuclease degradation are explored. For TF detection in vivo, I describe a successful strategy to internalise fluorescently labeled molecules into live E.coli. Viability and internalisation efficiency are characterised and ensemble measurements with FRET standards are demonstrated. Importantly, sm FRET measurements in vivo are achieved opening many exciting possibilities. The FRET based TF sensor is then internalised as a step towards real-time in vivo monitoring of TF concentrations. Finally a system based on DNA nanotechnology is presented for the non-covalent encapsulation and release of TFs. Such a system could be delivered into a cell to alter levels of gene expression using external stimuli as inputs. We believe these tools will generate valuable information in the study of prokaryotic gene expression as well as providing a potential commercial avenue towards diagnostics.

Protein-protein recognition plays a central role in the surveillance of self and non-self in the mammalian immune system and ultimately in cellular survival within the organism. Two systems of fundamental importance to the immune system are the Tumour Necrosis Factor (TNF) and the T cell receptor (TCR) families. High-throughput methods developed within the Oxford Protein Production Facility have been successfully applied to the production of members of the TNF receptor and ligand superfamilies for structural characterisation. The TNF receptor DR6 was successfully refolded from E.coli inclusion bodies using a rapid-dilution technique and yielded diffraction quality crystals. Data collected from these crystals will be used to obtain an x-ray crystallographic model of DR6. Vascular Endothelial Growth Inhibitor (VEGI) was produced as a soluble recombinant protein in E.coli, and formed a number of poorly diffracting crystals, it is hoped that further trials and optimization of conditions will lead to improved data quality. Lymphotoxin β receptor was produced in a Eukaryotic system. This has shed light on the complications posed by signal peptide cleavage and glycosylation on the production of protein for crystallization trials. TNF superfamily proteins are ideal targets for the design of novel therapeutic agents due to their involvement in a number of disease pathologies. Various methods of molecular docking and small molecule design were applied to the search for potential inhibitors of receptor binding for the TNF ligand proteins TRAIL and BAFF. A number of potential drug leads were identified from the National Cancer Institute drug database. The Natural Killer (NK) T cell restricted TCRs recognise CD1d-presented glycolipid. Determination of the crystal structures of the invariant NK TCR and the NK restricted TCRs 5E and 5B shows that these proteins adopt the canonical structures of class I MHC restricted TCRs. This suggests that the binding of CD1d-glycolipid by these receptors will conform to the same model of binding seen for the class I MHC restricted TCRs.

Foot-and-mouth disease virus (FMDV) is an economically devastating and highly contagious livestock pathogen. It exists as seven serotypes, comprising numerous antigenically distinct subtypes. The large amount of antigenic heterogeneity has confounded attempts at developing broadly reactive vaccines. In order to overcome this issue the fundamentals of the interactions between the virus and the host humoral immune response must first be understood. Previous work in this area using monoclonal antibody (mAb) escape mutants has identified five antigenic sites for the O serotype and efforts have been made to quantify their relative importance. However, this does not represent a complete picture of serotype O antigenicity. The work conducted in this thesis demonstrates the role of a limited number of dominant substitutions in mediating the antigenic diversity of serotype O Foot-and-Mouth disease virus. Two alternative but complementary methods for identifying epitopes were developed. The first used a mathematical model to analyse newly generated serological and sequence data from 105 viruses, cultured for this purpose (and cross-reacted to 5 reference antisera), in the context of an existing crystallographic structure to identify and quantify the antigenic importance of sites on the surface of the virus. The second approach was purely structural, using existing B cell epitope prediction tools to develop a method for predicting FMDV epitopes using existing crystallographic structures of FMDV. These techniques were validated by the use of reverse genetics, which confirmed the impact on cross reactivity of two predicted novel serotype O antigenic residues, with a further four novel residues identified by looking in depth at the interactions between two genetically close, but antigenically distant viruses. This increased knowledge of the antigenic composition of serotype O FMDV contributes to our understanding of the nature of vaccine efficacy and the breadth of protection, which, in the longer term, will aid in the goal of developing vaccines to better protect livestock from such a highly antigenically variable disease.

Deregulation of protein kinases is associated with many diseases making them important targets for therapeutic intervention. Kinases can switch between active and inactive conformations that can be targeted by type 1 or type 2 inhibitors respectively. One of the most relevant conformational switches is the ‘in’ and ‘out’ movement of the ATP/Mg2+ binding motif DFG. Factors modulating the conformational equilibria such as the residue environment of regulatory motifs remain poorly understood despite their importance for drug discovery. In this thesis, the first model system tested the hypothesis that accessibility of the DFG-out conformation is restricted by the energetic cost of transition between the in and out states. CDK2 was chosen as a target that was thought to have an inaccessible DFG-out conformation, and several point mutations were introduced to promote this conformational transition. Detailed biochemical and biophysical characterisation illustrated that the mutants bound type 2 inhibitors more potently than the wild type. In addition, the wild-type CDK2 was shown to bind type 2 inhibitors in the absence, but not in the presence, of cyclin. The first known CDK2 co-crystal structure in the DFG-out conformation was solved, opening the door to a new class of CDK2 inhibitors. In the second project, site-directed mutagenesis was used to explore the residues determining inhibitor selectivity between PIM1 and PIM2. Evaluation of ligand binding to the variants and comparison of PIM1 and PIM2 crystal structures showed that flexibility of the phosphate-binding loop was the dominant factor determining the differences in their affinities for ATP and small molecule inhibitors. These studies illustrate that residues contributing to kinase conformational equilibria can be just as important for inhibitor binding as contact residues formed in the ligand complex.

There is a strong need to develop a mechanical method to apply external torque to the bacterial flagellar motor. Such a method will allow us to probe the behaviour of the motor at a range of different speeds under different external conditions. In this thesis, I explored various methods to deliver torque at the single-molecule level, in particular the use of angular optical trapping and magnetic tweezers. I have identified rutile particles as suitable handles for use in angular optical trapping due to their high birefringence. Further progress was not achieved using angular optical trapping due to the lack of a suitable method to attach birefringent particles to the bacterial flagellar motor. On the other hand, I was able to make further progress using magnetic tweezers. A highly-reproducible and high-yielding magnetic bead assay was developed along with electromagnets capable of generating fast-rotating magnetic fields at magnitudes on the order of tens of mT. Using the system of delivering magnetic torque developed, I was able to stall and rotate the motor forward at speeds up to 220 Hz and in the reverse direction. Stalling experiments carried out on the motor revealed the stator mechanosensing depends on torque and not rotation. Signatures of stators dropping out at low load experiments further confirm the load dependence of stators.

This thesis addresses gaps that exist in the theory and knowledge of ancient DNA (aDNA). Much of the underlying basis of the field has been neglected in the excitement that followed the first aDNA studies. Therefore the results of many studies have been based on untested assumptions about the nature of post mortem DNA damage, sample preservation, contamination, and the efficacy of sample decontamination techniques. The validity of such results is questionable if the assumptions prove false. Hydrolytic post mortem DNA damage may modify recovered aDNA sequences. This thesis reports new insights into the biochemical basis of, predisposition of certain sequences and nucleotide positions towards, and subsequent effects of, such damage. Parallels of post mortem damage with in vivo mutation also enable insights into DNA sequence evolution. The long-term survival of DNA, and contamination of samples with exogenous DNA are two related problems characteristic to aDNA. The survival of endogenous DNA within bone, teeth and hair samples, the susceptibility of such samples to contamination, and the efficacy of decontamination techniques used to remedy such problems are investigated. The results highlight serious flaws in using bone and teeth as a DNA source. In contrast, the results demonstrate that hair may present a valuable DNA source for future studies. Numerous studies have reported the retrieval of ancient pathogen DNA from human samples. Analyses of the DNA content within teeth extracted from putative victims of the 2^nd plague argue that such studies are at great risk from DNA degradation, and contamination arising due to environmental microorganisms. An extrapolation of these results using basic physical and chemical theory is used to evaluate the potential survival of aDNA in ancient Egyptian remains. This suggests that positive results from such samples are unlikely.

No description available.

The influenza A virus genome consists of eight single-stranded segments of negativesense viral RNA (vRNA) with highly conserved, partially complementary termini. These termini associate in a double-stranded RNA structure, known as a panhandle, which is bound by the viral RNA-dependent RNA polymerase and can serve as a promoter in both viral transcription and replication. In part A of this thesis, I use a combination of classical biochemistry techniques and fluorescence techniques (both at the ensemble and single-molecule level) for a quantitative investigation of the interaction between purified influenza A RNA polymerase and the individual 5' and 3' conserved termini of the vRNA segments, as well as the double-stranded vRNA promoter. Furthermore, I report the first direct, real-time observation of the promoter changing its structure when bound by the polymerase and show that the structure assumed agrees best with the corkscrew model. In part B of this thesis, I use fluorescence to detect RNA: I design and test a singlemolecule biosensor aimed at probing the presence of influenza A RNA in a sample, on the one hand, and I use click-chemistry to fluorescently label very shorty RNAs (3-25nt) that have been generated in an in vitro transcription reaction, on the other. The biosensing assay I propose can be further developed for diagnostic purposed, while click-chemistry labelling of short RNAs can be optimised and extended such that it becomes a reliable alternative to the use of radiolabels.

The overall goal of my work was to develop and apply new chemical methods for the study of epigenetic DNA and protein modifications. In Chapter 3 the development of Suzuki-Miyaura cross coupling (SMcc) for the post-synthetic modification of DNA is described. DNA modification by SMcc is efficient (4-6h) and proceeds under mild conditions (37°C, pH 8.5). The incorporation of various groups useful for biological investigations is demonstrated using this methodology. Using a photocrosslinker, introduced into the DNA by SMcc capture experiments are performed to identify potential binding partners of modified DNA. In Chapter 4 a dehydroalanine (Dha) based chemical protein modification method is described that enables the introduction of posttranslational modification (PTM) mimics into histones. The PTM mimics introduced by this method are tested using western- and dot-blot and binding and enzymatic assays, confirming they function as mimics of the natural modifications. Chapter 5 describes the use of a generated PTM mimics to elucidate the function of O-linked β-Nacetylglucosamine (GlcNAc) of histones in transcriptional regulation. It is shown that GlcNAcylation of Thr-101 on histone H2A can destabilize nucleosome by modulating the H2A/B dimer – H3/H4 tetramer interface. N- and C-terminal histone tails play an important role in transcriptional regulation. In Chapter 6, nuclear magnetic resonance is used to investigate the structure of the histone H3 N-terminal tail in a nucleosome. The H3 tail, while intrinsically disordered, gains some α-helical character and adopts a compact conformation in a nucleosome context. This H3 tail structure is shown to be modulated by Ser-10 phosphorylation. The effect of a new covalent DNA modification, 5- hydroxymethylcytosine (5hmC), on transcription factor binding is investigated in Chapter 7. 5hmC influences HIF1α/β, USF and MAX binding to their native recognition sequence, implying involvement of this modification in epigenetic regulation.

This thesis describes my investigations into the principles underlying self-assembly of DNA origami nanostructures and discusses how these principles may be applied. To study the origami folding process I designed, synthesized and characterized a polymorphic tile, which could adopt various shapes. The distribution of tile shapes provided new insights into assembly. The origami tiles I studied were based on scaffolds derived from customized plasmids, which I prepared using recombinant DNA technology. I developed a technique to monitor incorporation of individual staples in real time using fluorescence, measuring small differences in staple binding temperatures (~0.5-5 °C). I examined the tiles using Atomic Force Microscopy and I found that a remarkably high proportion of polymorphic tiles folded well, which suggests that there are assembly <b>pathways</b>, arising from strong cooperation between staples. In order to analyse the tile shapes quantitatively, I developed a specialized image processing technique. For validation of the method, I generated and analysed simulated data, and the results confirmed that I could measure individual tile parameters with sub-pixel resolution. I studied eleven variants of the polymorphic tile, and I proved that minor staple modifications can be used to change the folding pathway dramatically. The strength of cooperation between staples affects their behaviour, which is also influenced by their length and base sequences. Paired staples are particularly significant in assembly, and there are clear parallels with protein folding. I describe in an Appendix how I applied origami assembly principles in the development of my concept for an autonomous rotary nanomotor utilizing the sequential opening of DNA hairpins (already used for linear motors). This device represents an advance over non-autonomous rotary motors and I have simulated its performance. In this thesis I have answered important questions about DNA origami assembly, and my findings could enable the development of more sophisticated DNA nanostructures for specific purposes.