<p><i>Staphylococcus aureus</i> (<i>S. aureus</i>) is a Gram-positive pathogen that causes a wide range of infections in both hospitals and communities, of which the total mortality rate is higher than AIDS, tuberculosis, and viral hepatitis combined. The drug resistant <i>S. aureus </i>is a member of the “ESKAPE” pathogens that require immediate and sustained actions of novel method to combat. However, the current antimicrobial development against <i>S. aureus</i> is in stagnation, which underscores the urgent need for novel antimicrobial scaffolds and targets. <i>S. aureus</i> Ribonuclease P protein (RnpA) is an essential protein that plays important roles in both tRNA maturation and mRNA degradation pathways. The goal of this research was to evaluate RnpA as an antimicrobial target using biophysical methods. The crystal structures of wild-type RnpA in three different constructs were determined, among which the tag-free RnpA construct has a structural model of 2.0 Å resolution and R_crys/R_free= 0.214/0.234, and its crystals are reproducible. This crystal structure of tag-free <i>S. aureus </i>RnpA shows a globular representation with key structural motifs, including the “RNR” Ribonuclease P RNA binding region and a substrate binding central cleft, which shares high similarity to previously solved RnpA structures from other species despite of their low sequence identity. Meanwhile, in a screen of <i>S. aureus </i>RnpA mutants performed by our collaborator, RnpA^P89A was found lacking the mRNA degradation activity while retaining the tRNA maturation function, and causing defects in cell viability. We therefore studied this mutant using differential scanning fluorimetry, crystallography, and circular dichroism. It was shown that RnpA^P89A is thermally less stable than wild-type RnpA by ~2.0 ˚C, but no secondary structural or 3D conformational differences were found between the two proteins. Although the mutant RnpA^P89A requires further characterization, the results of the studies in this thesis have begun to shed light on the relatively new role of <i>S. aureus </i>RnpA in mRNA degradation, and will serve as useful tools in future structure-based drug discovery for multi-drug resistant <i>S. aureus </i>treatment. </p>

As interações moleculares, em especial as de caráter não-covalente, são processos-chave em vários aspectos da biologia celular e molecular, desde a comunicação entre as células ou da velocidade e especificidade das reações enzimáticas. Portanto, há a necessidade de estudar e criar métodos preditivos para calcular a afinidade entre moléculas nos processos de interação, os quais encontram uma gama de aplicações, incluindo a descoberta de novos fármacos. No geral, entre esses valores de afinidade, o mais importante é a energia livre de ligação, que normalmente é determinada por modos computacionalmente rápidos, porém sem uma forte base teórica, ou por cálculos muito complexos, utilizando dinâmica molecular, onde mesmo com um grande poder de determinação da afinidade, é muito custoso computacionalmente. O objetivo deste trabalho é avaliar um modelo menos custoso computacionalmente e que promova um aprofundamento na avaliação de resultados obtidos a partir de simulações de docking molecular. Para esta finalidade, o método de Monte Carlo é empregado para a amostragem de orientações e conformações do ligante do sítio ativo macromolecular. A avaliação desta metodologia demonstrou que é possível calcular grandezas entrópicas e entálpicas e analisar a capacidade interativa entre complexos proteína-ligante de forma satisfatória para o complexo lisozima do bacteriófago T4. / The molecular interactions, especially the ones with a non-covalent nature, are key processes in general aspects of cellular and molecular biology, including cellular communication and velocity and specificity of enzymatic reactions. So, there is a strong need for studies and development of methods for the calculation of the affinity on interaction processes, since these have a wide range of applications like rational drug design. The free energy of binding is the most important measure among the affinity measurements. It can be calculated by quick computational means, but lacking on strong theoretical basis or by complex calculations using molecular dynamics, where one can compute accurate results but at the price of an increased computer power. The aim of this project is to evaluate a computationally inexpensive model which can improve the results from molecular docking simulations. For this end, the Monte Carlo method is implemented to sample different ligand configurations inside the macromolecular binding site. The evaluation of this methodology showed that is possible to calculate entropy and enthalpy, along analyzing the interactive capacity between receptor-ligands complexes in a satisfactory way for the bacteriophage T4.

Sistemas biológicos podem ser representados por redes que armazenam não apenas informações de conectividade, mas também informações de características de seus nós. No contexto biomolecular, esses nós podem representar proteínas, metabólitos, entre outros tipos de moléculas. Cada molécula possui características anotadas e armazenadas em bases de dados como o Gene Ontology. A comparação visual dessas redes depende de ferramentas que permitam o usuário identificar diferenças e semelhanças entre as anotações feitas sobre as moléculas (atributos) e também sobre as interações conhecidas (conexões). Neste trabalho de mestrado, buscou-se desenvolver técnicas que facilitem a comparação desses atributos sobre as moléculas, tentando manter no processo a visualização das redes em que essas moléculas estão inseridas. Como resultado, obteve-se a ferramenta VisPipeline-MultiNetwork, que permite comparar até seis redes, utilizando operações de conjuntos sobre as redes e sobre seus atributos. Dessa forma, diferentemente da maioria das ferramentas conhecidas para a visualização de redes biológicas, o VisPipeline-MultiNetwork permite a criação de redes cujos atributos são derivados das redes originais por meio de operações de união, intersecção e valores exclusivos. A comparação visual das redes é feita pela visualização do resultado dessas operações de conjuntos sobre as redes, por meio de um método de comparação lado-a-lado. Já a comparação dos atributos armazenados nos nós das redes é feita por meio de diagramas de Venn. Para auxiliar este tipo de comparação, a técnica InteractiVenn foi desenvolvida, em que o usuário pode interagir com um diagrama de Venn efetuando operações de união entre conjuntos. Essas operações de união aplicadas sobre os conjuntos são também aplicadas sobre as respectivas formas no diagrama. Esta característica da técnica a diferencia das outras ferramentas de criação de diagramas de Venn. Integrando essas funcionalidades, o usuário é capaz de comparar redes sob diversas perspectivas. Para exemplificar a utilização do VisPipeline-MultiNetwork, dois casos no contexto biomolecular foram estudados. Adicionalmente, uma ferramenta web para a comparação de listas de cadeias de caracteres por meio de diagramas de Venn foi desenvolvida. Ela também implementa a técnica InteractiVenn e foi denominada InteractiVenn website. / Biological systems can be represented by networks that store not only connectivity information, but also node feature information. In the context of molecular biology, these nodes may represent proteins, metabolites, and other types of molecules. Each molecule has features annotated and stored in databases such as Gene Ontology. A visual comparison of networks requires tools that allow the user to identify differences and similarities between nodes attributes as well as known interactions between nodes (connections). In this dissertation, we sought to develop a technique that would facilitate the comparison of these biological networks, striving to maintain in the process the visualization of the network connectivities. As a result, we have developed the VisPipeline-MultiNetwork tool, which allows comparison of up to six networks, using sets of operations on networks and on their attributes. Unlike most known tools for visualizing biological networks, VisPipeline-MultiNetwork allows the creation of networks whose attributes are derived from the original networks through operations of union, intersection and unique values. A visual comparison of the networks is achieved by visualizing the outcome of such joint operations through a all-in-one comparison method. The comparison of nodes attributes is performed using Venn diagrams. To assist this type of comparison, the InteractiVenn technique was developed, in which the user can interact with a Venn diagram, performing union operations between sets and their corresponding diagrams. This diagram union feature differs from other tools available for creating Venn diagrams. With these tools, users manage to compare networks from different perspectives. To exemplify the use of VisPipeline-MultiNetwork, two case studies were carried out in the biomolecular context. Additionally, a web tool for comparing lists of strings by means of Venn diagrams was made available. It also implements the InteractiVenn technique and its site has been named InteractiVenn.

Sistemas biológicos podem ser representados por redes que armazenam não apenas informações de conectividade, mas também informações de características de seus nós. No contexto biomolecular, esses nós podem representar proteínas, metabólitos, entre outros tipos de moléculas. Cada molécula possui características anotadas e armazenadas em bases de dados como o Gene Ontology. A comparação visual dessas redes depende de ferramentas que permitam o usuário identificar diferenças e semelhanças entre as anotações feitas sobre as moléculas (atributos) e também sobre as interações conhecidas (conexões). Neste trabalho de mestrado, buscou-se desenvolver técnicas que facilitem a comparação desses atributos sobre as moléculas, tentando manter no processo a visualização das redes em que essas moléculas estão inseridas. Como resultado, obteve-se a ferramenta VisPipeline-MultiNetwork, que permite comparar até seis redes, utilizando operações de conjuntos sobre as redes e sobre seus atributos. Dessa forma, diferentemente da maioria das ferramentas conhecidas para a visualização de redes biológicas, o VisPipeline-MultiNetwork permite a criação de redes cujos atributos são derivados das redes originais por meio de operações de união, intersecção e valores exclusivos. A comparação visual das redes é feita pela visualização do resultado dessas operações de conjuntos sobre as redes, por meio de um método de comparação lado-a-lado. Já a comparação dos atributos armazenados nos nós das redes é feita por meio de diagramas de Venn. Para auxiliar este tipo de comparação, a técnica InteractiVenn foi desenvolvida, em que o usuário pode interagir com um diagrama de Venn efetuando operações de união entre conjuntos. Essas operações de união aplicadas sobre os conjuntos são também aplicadas sobre as respectivas formas no diagrama. Esta característica da técnica a diferencia das outras ferramentas de criação de diagramas de Venn. Integrando essas funcionalidades, o usuário é capaz de comparar redes sob diversas perspectivas. Para exemplificar a utilização do VisPipeline-MultiNetwork, dois casos no contexto biomolecular foram estudados. Adicionalmente, uma ferramenta web para a comparação de listas de cadeias de caracteres por meio de diagramas de Venn foi desenvolvida. Ela também implementa a técnica InteractiVenn e foi denominada InteractiVenn website. / Biological systems can be represented by networks that store not only connectivity information, but also node feature information. In the context of molecular biology, these nodes may represent proteins, metabolites, and other types of molecules. Each molecule has features annotated and stored in databases such as Gene Ontology. A visual comparison of networks requires tools that allow the user to identify differences and similarities between nodes attributes as well as known interactions between nodes (connections). In this dissertation, we sought to develop a technique that would facilitate the comparison of these biological networks, striving to maintain in the process the visualization of the network connectivities. As a result, we have developed the VisPipeline-MultiNetwork tool, which allows comparison of up to six networks, using sets of operations on networks and on their attributes. Unlike most known tools for visualizing biological networks, VisPipeline-MultiNetwork allows the creation of networks whose attributes are derived from the original networks through operations of union, intersection and unique values. A visual comparison of the networks is achieved by visualizing the outcome of such joint operations through a all-in-one comparison method. The comparison of nodes attributes is performed using Venn diagrams. To assist this type of comparison, the InteractiVenn technique was developed, in which the user can interact with a Venn diagram, performing union operations between sets and their corresponding diagrams. This diagram union feature differs from other tools available for creating Venn diagrams. With these tools, users manage to compare networks from different perspectives. To exemplify the use of VisPipeline-MultiNetwork, two case studies were carried out in the biomolecular context. Additionally, a web tool for comparing lists of strings by means of Venn diagrams was made available. It also implements the InteractiVenn technique and its site has been named InteractiVenn.

The biodesulfurization 4S-pathway is a promising complementary enzymatic approach to remove sulfur from recalcitrant thiophenic derivatives in petroleum products that remain from conventional hydrodesulfurization method without diminishing the calorific value of oil. The final step of this pathway involves the carbon-sulfur bond cleavage from HBPS, and the production of the final products 2-hydroxybiphenyl (HBP) and sulfite, has been recognized as the rate-limiting step, partially as a result of product inhibition. However, the mechanisms and factors responsible for product inhibition in the last step have not been fully understood. In this work, we proposed a computational investigation using molecular dynamic simulations and free energy calculations on 2’-hydroxybiphenyl-2-sulfinate (HBPS) desulfinase (DszB) with different bound ligands as well as different solvent conditions to develop a fundamental understanding of the molecular-level mechanism responsible for product inhibition. Based on available crystal structures of DszB and biochemical characterization, we proposed a “gate” area close to substrate binding site of DszB is responsible for ligand egress and plays a role in product inhibition. We have conducted biphasic molecular dynamic simulations to evaluate the proposed gate area functionality. Non-bonded interaction energy analysis shows that hydrophobic residues around the gate area produce van der Waals interactions inhibiting translocation through the gate channel, and therefore, the molecules are easily trapped inside the binding site. Umbrella sampling molecular dynamics was performed to obtain the energy penalty associated with gate conformational change from open to close, which was 2.4 kcal/mol independent of solvent conditions as well as bound ligands. Free energy perturbation calculations were conducted for a group of six selected molecules bound to DszB. The selections were based on functional group representation and to calculate binding free energies that were directly comparable to experimental inhibition constants, KI. Our work provides a fundamental molecular-level analysis on product inhibition for the biodesulfurization 4S-pathway.

Naturally occurring enzymatic pathways enable highly specific, rapid thiophenic sulfur cleavage occurring at ambient temperature and pressure, which may be harnessed for the desulfurization of petroleum-based fuel. One pathway found in bacteria is a four-step catabolic pathway (the 4S pathway) converting dibenzothiophene (DBT), a common crude oil contaminant, into 2-hydroxybiphenyl (HBP) without disrupting the carbon-carbon bonds. 2’-Hydroxybiphenyl-2-sulfinate desulfinase (DszB), the rate-limiting enzyme in the enzyme cascade, is capable of selectively cleaving carbon-sulfur bonds. Accordingly, understanding the molecular mechanisms of DszB activity may enable development of the cascade as industrial biotechnology. Based on crystallographic evidence, we hypothesized that DszB undergoes an active site conformational change associated with the catalytic mechanism. Moreover, we anticipated this conformational change is responsible, in part, for enhancing product inhibition. Rhodococcus erythropolis IGTS8 DszB was recombinantly produced in Escherichia coli BL21 and purified to test these hypotheses. Activity and the resulting conformational change of DszB in the presence of HBP were evaluated. The activity of recombinant DszB was comparable to the natively expressed enzyme and was competitively inhibited by the product, HBP. Using circular dichroism, global changes in DszB conformation were monitored in response to HBP concentration, which indicated that both product and substrate produced similar structural changes. Molecular dynamics (MD) simulations and free energy perturbation with Hamiltonian replica exchange molecular dynamics (FEP/λ-REMD) calculations were used to investigate the molecular-level phenomena underlying the connection between conformation change and kinetic inhibition. In addition to the HBP, MD simulations of DszB bound to common, yet structurally diverse, crude oil contaminates 2’2-biphenol (BIPH), 1,8-naphthosultam (NTAM), 2-biphenyl carboxylic acid (BCA), and 1,8-naphthosultone (NAPO) were performed. Analysis of the simulation trajectories, including root mean square fluctuation (RMSF), center of mass (COM) distances, and strength of nonbonded interactions, when compared with FEP/λ-REMD calculations of ligand binding free energy, showed excellent agreement with experimentally determined inhibition constants. Together, the results show that a combination of a molecule’s hydrophobicity and nonspecific interactions with nearby functional groups contribute to a competitively inhibitive mechanism that locks DszB in a closed conformation and precludes substrate access to the active site. Limitations in DszB’s potential applications in industrial sulfur fixation are not limited to turnover rate. To better characterize DszB stability and to gain insight into ways by which to extend lifetime, as well as to pave the way for future studies in inhibition regulation, we evaluated the basic thermal and kinetic stability of DszB in a variety of solvation environments. Thermal stability of DszB was measured in a wide range of different commercially available buffer additives using differential scanning fluorimetry (DSF) to quickly identify favorable changes in protein melting point. Additionally, a fluorescent kinetic assay was employed to investigate DszB reaction rate over a 48 hr time period in a more focused group of buffer to link thermal stability to DszB life-time. Results indicate a concerningly poor short-term stability of DszB, with an extreme preference for select osmolyte buffer additives that only moderately curbed this effect. This necessitates a means of stability improvement beyond alteration of solvation environment. To this end, a more general investigation of glycosylation and its impact on protein stability was performed. Post-translational modification of proteins occurs in organisms from all kingdoms life, with glycosylation being among the most prevalent of amendments. The types of glycans attached differ greatly by organism but can be generally described as protein-attached carbohydrate chains of variable lengths and degrees of branching. With great diversity in structure, glycosylation serves numerous biological functions, including signaling, recognition, folding, and stability. While it is understood that glycans fulfill a variety of important roles, structural and biochemical characterization of even common motifs and preferred rotamers is incomplete. To better understand glycan structure, particularly their relevance to protein stability, we modeled and computed the solvation free energy of 13 common N- and O-linked glycans in a variety of conformations using thermodynamic integration. N-linked glycans were modeled in the β-1,4-linked conformation, attached to an asparagine analog, while O-linked glycans were each modeled in both the α-1,4 and β-1,4-linked conformations attached to both serine and threonine analogs. Results indicate a strong preference for the β conformation and show a synergistic effect of branching on glycan solubility. Our results serve as a library of solvation free energies for fundamental glycan building blocks to enhance understanding of more complex protein-carbohydrate structures moving forward.

The objective of this thesis was to investigate BiOWiSHTM-Aqua, a commercial dry solid formulation containing a consortium of bacteria and yeast, as a biopesticide for treatment of Botrytis cinerea, a gray mold that affects strawberries. BiOWiSHTM-Aqua was compared with another commercial product specifically used as a fungicide and bacteriocide, Serenade® Garden Disease Control Spray (concentrated Bacillus subtilis strain QST 713). Both laboratory tests as well as in vivo lab tests were conducted. BiOWiSHTM-Aqua results varied widely from plate to plate, regardless of experimental conditions. In some of these plates, inhibition zones were observed around colonies from BiOWiSHTM-Aqua, indicating efficacy. The organism responsible for the inhibition zones of B. cinerea growth was isolated from BiOWiSHTM-Aqua, and 16s rRNA analysis identified this culture as a strain of B. subtilis. This strain was designated as B. subtilis ssp. KLB. The B. subtilis KLB concentration required to completely inhibit B. cinerea was 9.1x104 CFU/mL when B. subtilis KLB was inoculated 48 hours before B. cinerea, 1.3x105 CFU/mL at 24 hours, and 3.2x106 CFU/mL when both were inoculated at the same time. Various preliminary experiments using B. subtilis KLB were also conducted to investigate its economic feasibility, to characterize the organism, and to test its post-harvest in vivo viability. B. subtilis KLB cell concentration was 1.6x109 CFU/mL in a bioreactor with LB at the end of the log growth phase. B. subtilis KLB achieved cell concentrations as high as 5x109 CFU/mL in shake flasks with food-grade tapioca as a carbon source. Inoculation of B. subtilis KLB on post-harvest strawberries did not have an effect on Botrytis infection rates compared to the negative control. These various experiments were the first step in research to potentially produce B. subtilis KLB on a commercial scale.

The potential value of the chitin biomass (e.g. food waste) is recently considered being ignored by landfill. Chitin can be a potential cheap carbon source for converting into value-added chemicals by microorganisms. Serratia marcescens is a chitinolytic bacterium that harbors endogenous chitinase systems. With goals of characterzing S. marcescens chitinolytic capabilities and applying S. marcescens to chemical production from chitin, my dissertation main content includes five chapters: 1) Chapter 1 highlights background information of chitin source, S. marcescens and potential metabolic engineering targets using chitin as a substrate; 2) Chapter 2 demonstrates that ChiR is a key regulator in regulating 9 chitinase-related genes in S. marcescens Db11 and manipulation of chiR can be a useful and efficient genetic target to enhance chitin utilization; 3) Chapter 3 reports the production of N-acetylneuraminic acid (Neu5Ac) from chitin by a bottom-up approach of engineering the nonconventional chitinolytic bacterium, Serratia marcescens, including native constitutive promoter characterization and transcriptional and translational pathway balancing; 4) Chapter 4 describes improvement of S. marcescens chitinolytic capability by an adaptive evolution approach; 5) Chapter 5 elucidates S. marcescens intracellular metabolite profile using a constraint-based genome-scale metabolic model (iSR929) based on genomic annotation of S. marcescens Db11. Overall, the dissertation work is the first report of demonstrating the concept of chitin-based CBP using S. marcescens and the computational model and genetic molecular tools developed in this dissertation are valuable but not limited to design-build-test of S. marcescens for contributing to the field of biological science and metabolic engineering applications.

There has been significant interest in developing dry adhesives mimicking the gecko adhesive system, which offers several advantages compared to conventional pressure sensitive adhesives. Specifically, gecko adhesive pads have anisotropic adhesion properties: the adhesive pads (spatulae) stick strongly when sheared in one direction but are non-adherent when sheared in the opposite direction. This anisotropy property is attributed to the complex topography of the array of fine tilted and curved columnar structures (setae) that bear the spatulae. In this thesis, easy, scalable methods, relying on conventional and unconventional techniques are presented to incorporate tilt in the fabrication of synthetic polymer-based dry adhesives mimicking the gecko adhesive system, which provide anisotropic adhesion properties. In the first part of the study, the anisotropic adhesion and friction properties of samples with various tilt angles to test the validity of a nanoscale tape-peeling model of spatular function are measured. Consistent with the Peel Zone model, samples with lower tilt angles yielded larger adhesion forces. Contact mechanics of the synthetic array were highly anisotropic, consistent with the frictional adhesion model and gecko-like. Based on the original design, a new design of gecko-like dry adhesives was developed which showed superior tribological properties and furthermore showed anisotropic adhesive properties without the need for tilt in the structures. These adhesives can be used to reversibly suspend weights from vertical surfaces (e.g., walls) and, for the first time to our knowledge, horizontal surfaces (e.g., ceilings) by simultaneously and judiciously activating anisotropic friction and adhesion forces. Furthermore, adhesion properties between artificial gecko-inspired dry adhesives and rough substrates with varying roughness are studied. The results suggest that both adhesion and friction forces on a rough substrate depends significantly on the geometrical parameters of the substrate. The results in this study may be helpful for understanding how geckos overcome the influence of natural surface roughness. The novel designs of our dry adhesives open the way for new gecko-like adhesive surfaces and articulation mechanisms that do not rely on intensive nanofabrication. / acase@tulane.edu

The use of ethanol as an additive to gasoline fuel is becoming a common phenomenon. It helps solve the energy crisis and environmental issues that fossil fuel has brought about. However, when dissolved in motor oil, ethanol would dilute motor oil and drastically change its lubrication properties, in the same manner as gasoline dilution. Since ethanol has higher boiling point than gasoline, it takes longer time to be cooked away from the oil, causing more severe changes to motor oil properties. In this work, a new analytical method is presented to study the behaviour of ethanol/oil system. Seven motor oil formulations provided by Italian group E.n.i. are tested regarding their performance in resisting ethanol dilution. The tests are conducted in microcapillaries within which ethanol droplet dissolves in motor oil phase under 40oC or 60oC. Mathematical model is developed to study the shrinkage kinetics of ethanol droplets. And, the mass transfer coefficients of ethanol transporting to different oil formulations are obtained. Similar experiments are conducted on hexadecane and new and used Shell SAE 5W-30 motor oil to discover the difference between motor oil and pure hydrocarbon and the difference between new motor oil and used motor oil. It was found through hexadecane tests and Shell motor oil tests that hydrocarbons with shorter chain length were less capable of resisting ethanol dilution; old motor oil are slower in dissolving ethanol than new oil; and, suspected ethanol-soot complex may form in old motor oil, which might corrode engine parts. / acase@tulane.edu