Browsing by Subject "Proteins"

Objectives

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Natural products belonging to the lipid II-binding family act as potent antimicrobial agents by disrupting cell wall biosynthesis via sequestering the late-stage intermediate lipid II. However, the emergence of resistance mechanisms and poor bioavailability have hindered the utility of these molecules as promising therapeutic intervention strategies to combat pathogenic bacterial infections. Gaining a deeper understanding of structural components and biosynthetic pathways can lead to the creation of second-generation derivatives to improve bioactivity and pharmacological properties. To explore this superfamily, we have used bioanalytical, biochemical, synthetic, computational, and enzymatic approaches that have been applied to three distinct projects. The first includes efforts to characterize the relationship between structural feature and bioactivity for the lipid II-binding CDA (calcium dependent antibiotic), malacidin. Through a series of minimally complex analogs, we determined non-proteinogenic amino acids and the N-acyl fatty acid moiety are essential for bioactivity. For the second project, we investigated a conserved mechanism of action for phylogenetically-related natural products within the lasso peptide subfamily. This work led to the discovery of a novel class I lasso peptide, arcumycin, and we validated a conserved mechanism of action for Actinobacteria-produced lasso peptides in targeting lipid II biosynthesis. Our last project sought to elucidate the mechanism of lipoinitiation for the ramoplanin family of molecules. Through a series of bioactivity assays, we found the transfer to the acyl carrier protein (ACP) in a fatty acyl-AMP ligase (FAAL)-dependent manner determined the specificity of lipids selected in the biosynthetic process. Collectively, through each project we have gained a deeper understanding of the structural elements and biosynthetic pathways of lipid II-binding antimicrobials.

Nanoparticles are being used or implemented in a wide array of applications including health care, cosmetics, automotive, food, beverage, coatings, consumer electronics, and coatings. Despite this widespread use, we are unable to predict how nanoparticles will interact with biological systems. This is important for both nanotoxicity resulting from human exposure to nanomaterials and the development of new nano-based biotechnologies. The first step in the interaction of nanoparticles with biological systems is often with blood, for biomedical applications, or lung fluid, when nanoparticles are inhaled. In both cases, the nanoparticles are exposed to proteins that form a "corona" by adsorbing on the nanoparticle surface. The subsequent cellular response is determined by this protein corona rather than the bare nanoparticle.Our goal is to develop a predictive capability for protein-nanoparticle interactions. This requires lab automation, large datasets, machine learning, and mechanistic studies. We first developed and validated a semi-automated approach to generate, purify, and characterize protein coronas using a liquid handling robot and low-cost proteomics. Using this semi-automated approach, we characterized the formation of protein coronas with increasing incubation time and serum concentration. Incubation time was found to be an important parameter for corona composition and concentration at high incubation concentrations but yielded only a small effect at low serum incubation concentrations. To better understand how the protein corona affects biological responses, we investigated the response of macrophage cells to titanium dioxide nanoparticles as a function of the protein corona. As in our previous work with serum proteins, we measured the concentration and composition of murine lung fluid proteins adsorbed on the surface of titanium dioxide nanoparticles. We found that a low concentration of lung fluid corona, relative to fetal bovine serum and bovine serum albumin coronas, led to an increased expression of cytokines (interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-α), and macrophage inflammatory protein 2 (MIP-2)), indicating an inflammation response. This underscores the importance of understanding how the composition and concentration of the protein corona governs organism responses to nanoparticle exposures. Our validated high-throughput lab automation work allowed us to synthesize a library of magnetic nanoparticles and characterize their resulting protein coronas. The resulting nanoparticle dataset has 12 unique NP surfaces, seven surface charges, two core sizes, and two core materials. We used this dataset to generate and characterize, via proteomics, a variety of protein coronas varying incubation concentration and purification methods. We used the resulting proteomic dataset in conjunction with a database of protein physicochemical properties to build a machine learning model that identifies the most important nanoparticle and protein properties for protein corona formation. The model was tested using external datasets and found that it can predict human serum and lung fluid coronas on varying nanoparticle surfaces. Overall, this combination of lab automation, machine learning, and mechanistic analysis suggests that a generalizable understanding of the protein corona formation and its effects is forthcoming.

Chlamydia trachomatis is the obligate intracellular pathogen responsible for the most common bacterial sexually transmitted infection worldwide. While our front-line antibiotics have been historically successful in combatting chlamydial infections, emerging issues including treatment failure and chlamydial persistence necessitate the development of new therapeutic approaches. In this work, an enzyme-focused approach was devised to explore two of the intricate survival strategies of C. trachomatis: virulence and energy metabolism. We sought to employ biochemistry, enzymology, and chemical biology tools to interrogate enzyme functions and inform the design of new antichlamydial agents. To these ends, our efforts focused on characterization of the virulence-associated effector protein chlamydial protease-like activity factor (CPAF) and the futalosine pathway for menaquinone biosynthesis. Mechanistic analyses of CPAF zymogen maturation and peptide hydrolysis were performed that collectively classified CPAF as a serine protease with a catalytic tetrad. Analogs of the natural product salinosporamide A were subsequently explored as CPAF inhibitors. The futalosine pathway was discovered to be a source of novel antichlamydial targets through traditional and chemical genetics analyses in a HeLa cell model of chlamydial infection. The foundation was also established for studying a specific pathway enzyme, CT263, in a continuous coupled enzyme assay. Collectively, this dissertation has progressed our knowledge of several enzymes involved in critical processes for chlamydial pathogenicity and viability. The insights gained on a mechanistic level and in the context of chlamydial infection have laid the groundwork for pursuing virulence and energy metabolism enzymes as antichlamydial targets and for developing inhibitors of their activity, which are much-needed resources to combat this extremely prevalent sexually transmitted infection.