The Trypanosoma brucei sphingolipid synthase, an essential enzyme and a drug target

Sphingolipids are important structural components of eukaryotic membranes, in addition they and their precursors are involved in signal transduction processes. In eukaryotes the biosynthetic pathway of sphingolipid biosynthesis is largely conserved. However, whilst mammals produce sphingomyelin (SM) as the major phosphosphingolipid using the enzyme SM synthase, plants and many pathogenic fungi and protozoa synthesize inositol phosphorylceramide (IPC) by IPC synthase. This enzyme is a target for anti-fungal drugs and functional orthologues have recently been identified in the insect vector-bome pathogenic kinetoplastid protozoa. These parasites are responsible for a range of neglected diseases and Trypanosoma brucei are the cause human African trypanosomiasis in many regions of Africa. The available treatments for this disease are limited, often demonstrate severe side-effects and drug resistance is increasing. T. brucei sphingolipid synthase (TbSLS), a functional orthologue of the yeast IPC synthase, may be a target for novel anti protozoals drugs. Here I show that this enzyme functions as an IPC synthase both in vitro and ex vivo. Furthermore, the TbSLS is essential for parasite growth and can be inhibited in vitro by a known anti-fungal Perhaps most importantly this drug demonstrates rapid trypanocidal activity against bloodstream form parasites. Thus TbSLS is a promising drug targe

Exploring topological phonons in different length scales: microtubules and acoustic metamaterials

The topological concepts of electronic states have been extended to phononic systems, leading to the prediction of topological phonons in a variety of materials. These phonons play a crucial role in determining material properties such as thermal conductivity, thermoelectricity, superconductivity, and specific heat. The objective of this dissertation is to investigate the role of topological phonons at different length scales. Firstly, the acoustic resonator properties of tubulin proteins, which form microtubules, will be explored The microtubule has been proposed as an analog of a topological phononic insulator due to its unique properties. One key characteristic of topological materials is the existence of edge modes within the energy gap. These edge modes allow energy to be transferred at specific frequencies along the edges of the material, while the bulk remains unaffected. In the case of microtubules, its ability to store vibrational energy at its edges and the sensitivity to changes in local bulk structure align with the properties of topological insulators. Furthermore, the appearance of edge modes in topological phononic insulators is determined by the local interactions of the bulk material. Even small changes in the local structure can shift the resonant frequency of the edge mode or completely extinguish it. Similarly, the ability of microtubules to shorten or overcome energy barriers is greatly affected by changes in their local bulk structure. This suggests a parallel between the impact of local bulk structure on both topological insulators and microtubules. This similarity has led to the proposal that microtubules could serve as an analog of topological phononic insulators, providing insights into their dynamics and potential applications in fields such as chemotherapy drug development and nanoscale materials. Secondly, the application of topological phonons in the realm of acoustic metamaterials will be examined. Acoustic waves have recently become a versatile platform for exploring and studying various topological phases, showcasing their universality and diverse manifestations. The unique properties of topological insulators and their surface states heavily rely on the dimension and symmetries of the material, making it possible to classify them using a periodic table of topological insulators. However, certain combinations of dimensions and symmetries can impede the achievement of topological insulation. It is of utmost importance to preserve symmetries in order to maintain the desired topological properties, which necessitates careful consideration of coupling methods. In the context of discrete acoustic resonant models, efficiently coupling resonators while simultaneously preserving symmetry poses a challenging question. In this part, a clever experimental approach is proposed and discussed to couple acoustic crystals. This modular platform not only supports the existence of topologically protected edge and interface states but also offers a convenient setup that can be easily assembled and disassembled. Furthermore, inspired by recent theoretical advancements that draw on techniques from the field of C*-algebras for identifying topological metals, the present study provides direct observations of topological phenomena in gapless acoustic crystals. Through these observations, a general experimental technique is realized and developed to demonstrate the topology of such systems. By employing the method of coupling acoustic crystals, the investigation unveils robust boundary-localized states in a topological acoustic metal and presents a reinterpretation of a composite operator as a new Hamiltonian. This reinterpretation enables the direct observation of a topological spectral flow and facilitates the measurement of topological invariants. Through these investigations, the aim of this dissertation is to deepen our understanding of the significance and potential applications of topological phonons in diverse systems

The impact of empowerment on job satisfaction: A case study in a hotel

This study explores the impact of empowerment on job satisfaction based on a case study in a hotel. The purpose of this study was to determine the perceptions of employees in the subject hotel concerning empowerment and job satisfaction. Specially, the study addressed the following research questions: (1) To what extent do employees perceive that they are empowered? (2) To what extent do employees perceive they feel satisfied about their jobs? (3) To what extent does empowerment have an impact on job satisfaction? Additional analyses revealed different age, gender, education, ethnic background, length of service in the hotel industry, department and position of employees have an effect on perceptions about empowerment and job satisfaction. Recommendations for future research are discussed

A designed protein interface that blocks fibril formation

Protein fibril formation is implicated in many diseases, and therefore much effort has been focused toward the development of inhibitors of this process. In a previous project, a monomeric protein was computationally engineered to bind itself and form a heterodimer complex following interfacial redesign. One of the protein monomers, termed monomer-B, was unintentionally destabilized and shown to form macroscopic fibrils. Interestingly, in the presence of the designed binding partner, fibril formation was blocked. Here we describe the complete characterization of the amyloid properties of monomer-B and the inhibition of fiber formation by the designed binding partner, monomer-A. Both proteins are mutants of the betal domain of streptococcal protein-G. The free monomer-B protein forms amyloid-type fibrils, as determined by transmission electron microscopy and the change in fluorescence of Thioflavin T, an amyloid-specific dye. Fibril formation kinetics are influenced by pH, protein concentration, and seeding with preformed fibrils. Under all conditions tested, monomer-A was able to inhibit the formation of monomer-B fibrils. This inhibition is specific to the engineered interaction, as incubation of monomer-B with wild-type protein-G (a structural homologue) did not result in inhibition under the same conditions. Thus, this de novo-designed heterodimeric complex is an excellent model system for the study of protein-based fibril formation and inhibition. This system provides additional insight into the development of pharmaceuticals for amyloid disorders, as well as the potential use of amyloid fibrils for self-assembling nanostructures

A software architecture for autonomous spacecraft

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (leaf 47).by Jimmy S. Shih.M.Eng