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Description
Transient Receptor Potential (TRP) ion channels are a diverse family of nonselective, polymodal sensors in uni- and multicellular eukaryotes that are implicated in an assortment of biological contexts and human disease. The cold-activated TRP Melastatin-8 (TRPM8) channel, also recognized as the human body's primary cold sensor, is among the few

Transient Receptor Potential (TRP) ion channels are a diverse family of nonselective, polymodal sensors in uni- and multicellular eukaryotes that are implicated in an assortment of biological contexts and human disease. The cold-activated TRP Melastatin-8 (TRPM8) channel, also recognized as the human body's primary cold sensor, is among the few TRP channels responsible for thermosensing. Despite sustained interest in the channel, the mechanisms underlying TRPM8 activation, modulation, and gating have proved challenging to study and remain poorly understood. In this thesis, I offer data collected on various expression, extraction, and purification conditions tested in E. Coli expression systems with the aim to optimize the generation of a structurally stable and functional human TRPM8 pore domain (S5 and S6) construct for application in structural biology studies. These studies, including the biophysical technique nuclear magnetic spectroscopy (NMR), among others, will be essential for elucidating the role of the TRPM8 pore domain in in regulating ligand binding, channel gating, ion selectively, and thermal sensitivity. Moreover, in the second half of this thesis, I discuss the ligation-independent megaprimer PCR of whole-plasmids (MEGAWHOP PCR) cloning technique, and how it was used to generate chimeras between TRPM8 and its nearest analog TRPM2. I review steps taken to optimize the efficiency of MEGAWHOP PCR and the implications and unique applications of this novel methodology for advancing recombinant DNA technology. I lastly present preliminary electrophysiological data on the chimeras, employed to isolate and study the functional contributions of each individual transmembrane helix (S1-S6) to TRPM8 menthol activation. These studies show the utility of the TRPM8\u2014TRPM2 chimeras for dissecting function of TRP channels. The average current traces analyzed thus far indicate that the S2 and S3 helices appear to play an important role in TRPM8 menthol modulation because the TRPM8[M2S2] and TRPM8[M2S3] chimeras significantly reduce channel conductance in the presence of menthol. The TRPM8[M2S4] chimera, oppositely, increases channel conductance, implying that the S4 helix in native TRPM8 may suppress menthol modulation. Overall, these findings show that there is promise in the techniques chosen to identify specific regions of TRPM8 crucial to menthol activation, though the methods chosen to study the TRPM8 pore independent from the whole channel may need to be reevaluated. Further experiments will be necessary to refine TRPM8 pore solubilization and purification before structural studies can proceed, and the electrophysiology traces observed for the chimeras will need to be further verified and evaluated for consistency and physiological significance.
ContributorsWaris, Maryam Siddika (Author) / Van Horn, Wade (Thesis director) / Redding, Kevin (Committee member) / School of Molecular Sciences (Contributor) / Department of English (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
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Description
The FoF1 ATP synthase is a molecular motor critical to the metabolism of virtually all life forms, and it acts in the manner of a hydroelectric generator. The F1 complex contains an (αβ)3 (hexamer) ring in which catalysis occurs, as well as a rotor comprised by subunit-ε in addition to

The FoF1 ATP synthase is a molecular motor critical to the metabolism of virtually all life forms, and it acts in the manner of a hydroelectric generator. The F1 complex contains an (αβ)3 (hexamer) ring in which catalysis occurs, as well as a rotor comprised by subunit-ε in addition to the coiled-coil and globular foot domains of subunit-γ. The F1 complex can hydrolyze ATP in vitro in a manner that drives counterclockwise (CCW) rotation, in 120° power strokes, as viewed from the positive side of the membrane. The power strokes that occur in ≈ 300 μsec are separated by catalytic dwells that occur on a msec time scale. A single-molecule rotation assay that uses the intensity of polarized light, scattered from a 75 × 35 nm gold nanorod, determined the average rotational velocity of the power stroke (ω, in degrees/ms) as a function of the rotational position of the rotor (θ, in degrees, measured in reference to the catalytic dwell). The velocity is not constant but rather accelerates and decelerates in two Phases. Phase-1 (0° - 60°) is believed to derive power from elastic energy in the protein. At concentrations of ATP that limit the rate of ATP hydrolysis, the rotor can stop for an ATP-binding dwell during Phase-1. Although the most probable position that the ATP-binding dwell occurs is 40° after the catalytic dwell, the ATP-binding dwell can occur at any rotational position during Phase-1 of the power stroke. Phase-2 of the power stroke (60° - 120°) is believed to be powered by the ATP-binding induced closure of the lever domain of a β-subunit (as it acts as a cam shaft against the γ-subunit). Algorithms were written, to sort and analyze F1-ATPase power strokes, to determine the average rotational velocity profile of power strokes as a function of the rotational position at which the ATP-binding dwell occurs (θATP-bd), and when the ATP-binding dwell is absent. Sorting individual ω(θ) curves, as a function of θATP-bd, revealed that a dependence of ω on
θATP-bd exists. The ATP-binding dwell can occur even at saturating ATP concentrations. We report that ω follows a distinct pattern in the vicinity of the ATP-binding dwell, and that the ω(θ) curve contains the same oscillations within it regardless of θATP-bd. We observed that an acceleration/deceleration dependence before and after the ATP-binding dwell, respectively, remained for increasing time intervals as the dwell occurred later in Phase-1, to a maximum of ≈ 40°. The results were interpreted in terms of a model in which the ATP-binding dwell results from internal drag at a variable position on the γε rotor.
ContributorsBukhari, Zain Aziz (Author) / Frasch, Wayne D. (Thesis director) / Allen, James P. (Committee member) / Redding, Kevin (Committee member) / School of Molecular Sciences (Contributor) / Department of Physics (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
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Description
The two chapters of this thesis focus on different aspects of DNA and the properties of nucleic acids as the whole. Chapter 1 focuses on the structure of DNA and its relationship to enzymatic efficiency. Chapter 2 centers itself on threose nucleic acid and optimization of a step in the

The two chapters of this thesis focus on different aspects of DNA and the properties of nucleic acids as the whole. Chapter 1 focuses on the structure of DNA and its relationship to enzymatic efficiency. Chapter 2 centers itself on threose nucleic acid and optimization of a step in the path to its synthesis. While Chapter 1 discusses DNA and Uracil-DNA Glycosylase with regards to the base excision repair pathway, Chapter 2 focuses on chemical synthesis of an intermediate in the pathway to the synthesis of TNA, an analogous structure with a different saccharide in the sugar-phosphate backbone.
Chapter 1 covers the research under Dr. Levitus. Four oligonucleotides were reacted for zero, five, and thirty minutes with uracil-DNA glycosylase and subsequent addition of piperidine. These oligonucleotides were chosen based on their torsional rigidities as predicted by past research and predictions. The objective was to better understand the relationship between the sequence of DNA surrounding the incorrect base and the enzyme’s ability to remove said base in order to prepare the DNA for the next step of the base excision repair pathway. The first pair of oligonucleotides showed no statistically significant difference in enzymatic efficiency with p values of 0.24 and 0.42, while the second pair had a p value of 0.01 at the five-minute reaction. The second pair is currently being researched at different reaction times to determine at what point the enzyme seems to equilibrate and react semi-equally with all sequences of DNA.
Chapter 2 covers the research conducted under Dr. Chaput. Along the TNA synthesis pathway, the nitrogenous base must be added to the threofuranose sugar. The objective was to optimize the original protocol of Vorbrüggen glycosylation and determine if there were better conditions for the synthesis of the preferred regioisomer. This research showed that toluene and ortho-xylene were more preferable as solvents than the original anhydrous acetonitrile, as the amount of preferred isomer product far outweighed the amount of side product formed, as well as improving total yield overall. The anhydrous acetonitrile reaction had a final yield of 60.61% while the ortho-xylene system had a final yield of 94.66%, an increase of approximately 32%. The crude ratio of preferred isomer to side product was also improved, as it went from 18% undesired in anhydrous acetonitrile to 4% undesired in ortho-xylene, both values normalized to the preferred regioisomer.
ContributorsTamirisa, Ritika Sai (Author) / Levitus, Marcia (Thesis director) / Stephanopoulos, Nicholas (Committee member) / Windman, Todd (Committee member) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
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Description
With a quantum efficiency of nearly 100%, the electron transfer process that occurs within the reaction center protein of the photosynthetic bacteria Rhodobacter (Rh.) sphaeroides is a paragon for understanding the complexities, intricacies, and overall systemization of energy conversion and storage in natural systems. To better understand the way in

With a quantum efficiency of nearly 100%, the electron transfer process that occurs within the reaction center protein of the photosynthetic bacteria Rhodobacter (Rh.) sphaeroides is a paragon for understanding the complexities, intricacies, and overall systemization of energy conversion and storage in natural systems. To better understand the way in which photons of light are captured, converted into chemically useful forms, and stored for biological use, an investigation into the reaction center protein, specifically into its cascade of cofactors, was undertaken. The purpose of this experimentation was to advance our knowledge and understanding of how differing protein environments and variant cofactors affect the spectroscopic aspects of and electron transfer kinetics within the reaction of Rh. sphaeroides. The native quinone, ubiquinone, was extracted from its pocket within the reaction center protein and replaced by non-native quinones having different reduction/oxidation potentials. It was determined that, of the two non-native quinones tested—1,2-naphthaquinone and 9,10- anthraquinone—the substitution of the anthraquinone (lower redox potential) resulted in an increased rate of recombination from the P+QA- charge-separated state, while the substitution of the napthaquinone (higher redox potential) resulted in a decreased rate of recombination.
ContributorsSussman, Hallie Rebecca (Author) / Woodbury, Neal (Thesis director) / Redding, Kevin (Committee member) / Lin, Su (Committee member) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2015-12
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Description

Lyme disease is a common tick-borne illness caused by the Gram-negative bacterium Borrelia burgdorferi. An outer membrane protein of Borrelia burgdorferi, P66, has been suggested as a possible target for Lyme disease treatments. However, a lack of structural information available for P66 has hindered attempts to design medications to target

Lyme disease is a common tick-borne illness caused by the Gram-negative bacterium Borrelia burgdorferi. An outer membrane protein of Borrelia burgdorferi, P66, has been suggested as a possible target for Lyme disease treatments. However, a lack of structural information available for P66 has hindered attempts to design medications to target the protein. Therefore, this study attempted to find methods for expressing and purifying P66 in quantities that can be used for structural studies. It was found that by using the PelB signal sequence, His-tagged P66 could be directed to the outer membrane of Escherichia coli, as confirmed by an anti-His Western blot. Further attempts to optimize P66 expression in the outer membrane were made, pending verification via Western blotting. The ability to direct P66 to the outer membrane using the PelB signal sequence is a promising first step in determining the overall structure of P66, but further work is needed before P66 is ready for large-scale purification for structural studies.

ContributorsRamirez, Christopher Nicholas (Author) / Fromme, Petra (Thesis director) / Hansen, Debra (Committee member) / Department of Physics (Contributor) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description

Molecular engineering is an emerging field that aims to create functional devices for modular purposes, particularly bottom-up design of nano-assemblies using mechanical and chemical methods to perform complex tasks. In this study, we present a novel method for constructing an RNA clamp using circularized RNA and a broccoli aptamer for

Molecular engineering is an emerging field that aims to create functional devices for modular purposes, particularly bottom-up design of nano-assemblies using mechanical and chemical methods to perform complex tasks. In this study, we present a novel method for constructing an RNA clamp using circularized RNA and a broccoli aptamer for fluorescence sensing. By designing a circular RNA with the broccoli aptamer and a complementary DNA strand, we created a molecular clamp that can stabilize the aptamer. The broccoli aptamer displays enhanced fluorescence when bound to its ligand, DFHBI-1T. Upon induction with this small molecule, the clamp can exhibit or destroy fluorescence. We demonstrated that we could control the fluorescence of the RNA clamp by introducing different complementary DNA strands, which regulate the level of fluorescence. Additionally, we designed allosteric control by introducing new DNA strands, making the system reversible. We explored the use of mechanical tension to regulate RNA function by attaching a spring-like activity through the RNA clamp to two points on the RNA surface. By adjusting the stiffness of the spring, we could control the tension between the two points and induce reversible conformational changes, effectively turning RNA function on and off. Our approach offers a simple and versatile method for creating RNA clamps with various applications, including RNA detection, regulation, and future nanodevice design. Our findings highlight the crucial role of mechanical forces in regulating RNA function, paving the way for developing new strategies for RNA manipulation, and potentially advancing molecular engineering. Although the current work is ongoing, we provide current progress of both theoretical and experimental calculations based on our findings.

ContributorsJoseph, Joel (Author) / Yan, Hao (Thesis director) / Stephanopoulos, Nicholas (Committee member) / Lapinaite, Audrone (Committee member) / Barrett, The Honors College (Contributor) / Historical, Philosophical & Religious Studies, Sch (Contributor) / School of Molecular Sciences (Contributor)
Created2023-05
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Description
Receiving signals and responding to the environment is crucial for survival for every living organism. One of those signals is being able to detect environmental and visceral temperatures. Transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential melastatin 8 (TRPM8) are ion channels within cells that allow higher organisms

Receiving signals and responding to the environment is crucial for survival for every living organism. One of those signals is being able to detect environmental and visceral temperatures. Transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential melastatin 8 (TRPM8) are ion channels within cells that allow higher organisms to detect hot and cold temperatures, respectively. These TRP channels are also implicated in diverse physiological roles including pain, obesity, and cancer. As a result, these channels have garnered interest as potential targets for therapeutic interventions. However, the entanglement of TRPV1 and TRPM8 polymodal activation where it responds to a variety of different stimuli has caused adverse side effects of body thermal dysregulation and misregulation when antagonizing these channels as drug targets. This dissertation will dissect the molecular mechanism and regulation of TRPV1 and TRPM8. An in-depth look into the complex and conflicting results in trying to find the key area for thermosensation as well as looking into disentangling the polymodal activation modes in TRPV1. The regulatory mechanism between TRPM8 with phosphoinositide interacting regulator of TRPs (PIRT) and calmodulin will be examined using nuclear magnetic resonance (NMR). A computational, experimental, and methodical approach into ancestral TRPM8 orthologs using whole-cell patch-clamp electrophysiology, calcium mobilization assay, and cellular thermal shift assay (CETSA) to determine whether these modes of activation can be decoupled. Lastly, smaller studies are covered like developing a way to delivery full-length and truncated protein using amphipols to artificial and live cells without the biological regulatory processes and the purification of the TRPM8 transmembrane domain (TMD). In the end, two successful methods were developed to study the polymodal activation of proteins.
ContributorsLuu, Dustin Dean (Author) / Van Horn, Wade D (Thesis advisor) / Redding, Kevin E (Committee member) / Chiu, Po-Lin (Committee member) / Arizona State University (Publisher)
Created2023
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Description
The understanding of protein functions in vivo is very important since the protein is the building block of a cell. Cryogenic electron microscopy (cryo-EM) is capable of visualizing protein samples in their near-native states in high-resolution details. Cryo-EM enables the visualization of biomolecular structures at multiscale ranging from

The understanding of protein functions in vivo is very important since the protein is the building block of a cell. Cryogenic electron microscopy (cryo-EM) is capable of visualizing protein samples in their near-native states in high-resolution details. Cryo-EM enables the visualization of biomolecular structures at multiscale ranging from a cellular structure to an atomic structure of protein subunit.Neurodegenerative diseases, like Alzheimer’s disease and frontotemporal dementia, have multiple dysregulated signaling pathways. In my doctoral studies, I investigated two protein complexes relevant to these disorders: one is the proNGF- p75 neurotrophin receptor (p75NTR)- sortilin neurotrophin complex and the other is the p97R155H mutant complex. The neurotrophins are a family of soluble basic growth factors involved in the development, maintenance, and proliferation of neurons in the central nervous system (CNS) and peripheral nervous system (PNS). The ligand for the neuronal receptors dictates the fate of the neuronal cells. My studies focused on understanding the binding interfaces between the proteins in the proNGF-p75NTR-sortilin neuronal apoptotic complex. I have performed the biochemical characterization of the complex to understand how the complex formation occurs. Single amino-acid mutation of R155H on the N-domain of p97 is known to be the prevalent mutation in 40% patients suffering from neurodegenerative disease. The p97R155H mutant exhibits abnormal ATPase activity and cofactor dysregulation. I pursued biochemical characterization in combination with single-particle cryo-EM to explore the interaction of p97R155H mutant with its cofactor p47 and determined the full-length structures of the p97R155H-p47 assemblies for the first time. About 40% p97R155H organizes into higher order dodecamers, which lacks nucleotide binding, does not bind to p47, and closely resembles the structure of p97 bound with an adenosine triphosphate (ATP)-competitive inhibitor, CB-5083, suggesting an inactive state of the p97R155H mutant. The structures also revealed conformational changes of the arginine fingers which might contribute to the elevated p97R155H ATPase activity. Because the D1-D2 domain communication is important in regulating the ATPase function, I further studied the functions of the conserved L464 residue on the D1-D2 linker using mutagenesis and single-particle cryo-EM. The biochemical and structural results suggested the torsional constraint of the D1-D2 linker likely modulates the D2 ATPase activity. Our studies thus contributed to develop deeper knowledge of the intricate cellular mechanisms and the proteins affected in disease pathways.
ContributorsNandi, Purbasha (Author) / Chiu, Po-Lin (Thesis advisor) / Mazor, Yuval (Committee member) / Hansen, Debra T (Committee member) / Arizona State University (Publisher)
Created2022
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Description
G protein-coupled receptors (GPCRs) are known to be modulated by membrane cholesterol levels, but whether or not the effects are caused by specific receptor-cholesterol interactions or cholesterol’s general effects on the membrane is not well-understood. Results from coarse-grained molecular dynamics (CGMD) simulations coupled and structural bioinformatics offer new insights into

G protein-coupled receptors (GPCRs) are known to be modulated by membrane cholesterol levels, but whether or not the effects are caused by specific receptor-cholesterol interactions or cholesterol’s general effects on the membrane is not well-understood. Results from coarse-grained molecular dynamics (CGMD) simulations coupled and structural bioinformatics offer new insights into how cholesterol modulates GPCR function by showing cholesterol interactions with β2AR that agree with previously published data. Additionally, differential and specific cholesterol binding in the CCK receptor subfamily was observed while revealing a previously unreported Cholesterol Recognition Amino-acid Consensus (CRAC) sequence that is also conserved across 38% of class A GPCRs. Mutation of this conserved CRAC sequence of the β2AR affects cholesterol stabilization of the receptor in a lipid bilayer. Serial femtosecond crystallography (SFX) with X-ray free electron lasers (XFELs) has proven highly successful for structure determination of challenging membrane proteins crystallized in lipidic cubic phase, however, as most techniques, it has limitations. Using an optimized SFX experimental setup in a helium atmosphere we determined the room temperature structure of the adenosine A2A receptor (A2AAR) at 2.0 Å resolution and compared it with previous A2AAR structures determined in vacuum and/or at cryogenic temperatures. Specifically, we demonstrated the capability of utilizing high XFEL beam transmissions, in conjunction with a high dynamic range detector, to collect high-resolution SFX data while reducing crystalline material consumption and shortening the collection time required for a complete data set.
The results of these studies provide a better understanding of receptor-cholesterol interactions that can contribute to novel and improved therapeutics for a variety of diseases. Furthermore, the experimental setups presented herein can be applied to future molecular dynamics and SFX applications for protein nanocrystal samples to aid in structure-based discovery efforts of therapeutic targets that are difficult to crystallize.
ContributorsGeiger, James (Author) / Liu, Wei (Thesis advisor) / Mills, Jeremy (Committee member) / Chiu, Po-Lin (Committee member) / Arizona State University (Publisher)
Created2020
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Description
G protein-coupled receptors (GPCRs) are a large family of proteins involved in the cell signaling and regulation of many biological and pathological processes in the human body. To fully understand their functions, various approaches are needed. This work combines several techniques to advance the study of GPCRs with the overarching

G protein-coupled receptors (GPCRs) are a large family of proteins involved in the cell signaling and regulation of many biological and pathological processes in the human body. To fully understand their functions, various approaches are needed. This work combines several techniques to advance the study of GPCRs with the overarching goal of pursuing X-ray crystallization using lipidic cubic phase (LCP). In meso, or LCP crystallization method involves imbedding the GPCR into a lipid membrane-mimetic material which spontaneously forms when monoacylglycerols (MAGs) are mixed at the correct hydration level and temperature. It provides a stable environment for GPCRs and has been established as the most common method to resolve structural details of GPCRs (Chapter 2). Yet, before crystallization, GPCRs need to be put through several rounds of optimization of the construct design, including truncation of N- and C- termini, fusing different soluble proteins, and mutating the receptor (Chapter 3). Other methods were also used to gain structural insights into GPCR interactions, such as coarse-grained molecular dynamic simulations, which showed the specific regions of interactions with cholesterol molecules imbedded in the membranes (Chapter 4). This study demonstrated β2-adrenergic receptor (β2AR), a GPCR, as a model of a cholesterol-sensitive receptor. Mutations were made to test the effect of removing specific residues of interest on cholesterol stabilization through the LCP-Tm assay, producing results that align with the simulation data. Finally, the goal of the last study is to provide a guide to identify which host lipids form stable LCP phases for different applications (Chapter 5). Small angle X-ray scattering is used to identify phases in hundreds of different precipitant conditions in the search of suitable host lipid for LCP studies. The results present a systematic overview of the compatibility of common MAGs by screening them against different precipitant solutions including varying salts and polyethylene glycol (PEG) concentrations, different PEG sizes, the presence of detergent or protein in the sample, and the addition of cholesterol. Together, these studies present a variety of methods to advance the structural studies of GPCRs using LCP
ContributorsAL-SAHOURI, ZINA (Author) / Liu, Wei (Thesis advisor) / Stephanopoulos, Nicholas (Committee member) / Chiu, Po-Lin (Committee member) / Arizona State University (Publisher)
Created2021