The objective of this study was to determine whether the cataract-related G18V variant of human γS-crystallin has increased exposure of hydrophobic residues that could explain its aggregation propensity and/or recognition by αB-crystallin. We used an ANS fluorescence assay and NMR chemical shift perturbation to experimentally probe exposed hydrophobic surfaces. These results were compared to flexible docking simulations of ANS molecule to the solution-state NMR structures of γS-WT and γS-G18V. γS-G18V exhibits increased ANS fluorescence, suggesting increased exposed hydrophobic surface area. The specific residues involved in ANS binding were mapped by NMR chemical shift perturbation assays, revealing ANS binding sites in γS-G18V that are not present in $\gamma$S-WT. Molecular docking predicts three binding sites that are specific to γS-G18V corresponding to the exposure of a hydrophobic cavity located at the interdomain interface, as well as two hydrophobic patches near a disordered loop containing solvent-exposed cysteines, all but one of which is buried in γS-WT. Characterization of changes in exposed hydrophobic surface area between wild-type and variant proteins can help elucidate the mechanisms of aggregation propensity and chaperone recognition, presented here in the context of cataract formation.

γ-crystallins are structural eye lens proteins responsible for focusing light into the retina. These proteins are highly stable, being capable of remaining soluble at concentratins exceeding 300 g/L for an entire lifetime. Upon a loss in solubility, either by mutation or chemical damage to the protein structure, opaque aggregates form in the eye lens, known as cataract. Understanding the conformations and interactions of the γ-crystallins in their aggregated state will provide a deeper understanding of the mechanisms behind cataract formation.The work presented in this dissertation will investigate cataract-related sequences of γS- and γD-crystallins (γS-WT and γD-WT, respectively). Using molecular dynamics and other modeling techniques, I investigate potential sites for interprotein interaction, often through the exposure of hydrophobic residues. In the congenital cataract-related G18V variant of γS-crystallin (γS-G18V), the exposure of hydrophobic patches are identified in a relatively folded protein. Simulated protein-ligand conformations of a hydrophobic probe (ANS) identify hydrophobic sites both local and allosteric to the site of mutation. In the W42R variant of γD-crystallin (γD-W42R), a 17 μs molecular dynamics simulations shows the spontaneous separation of the N- and C-terminal domains (whereas γS-WT remains stable for 50 μs). Two protein simulations show that the hydrophobic interdomain interface becomes the main site for interprotein interaction, providing strong support for a domain swapping aggregation pathway at physiological conditions. The thermal stability is analyzed for the γS-crystallins of the human and Antarctic toothfish. The less thermally stable toothfish proteins show correlated increases in backbone flexibility and decreases in the packing of the hydrophobic core, yet maintain similar structure and dynamics at their native temperature. Finally, an analysis of the domain-domain motions in γD-WT fluctuations is performed in the presence and absence of macromolecular crowding. The autocorrelation function of the interdomain distance ages over 50 μs of simulation, showing non-convergent dynamics even after significant computational sampling.

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The goal of this dissertation is to study strongly correlated f–electron materials under extreme conditions using various novel imaging techniques. Strongly correlated electron materials exhibit complex physics, and when modified by a control parameter such as pressure, chemical composition, magnetic field, or temperature, can lead to novel quantum phases of matter. The underlying physics of these novel quantum phases of matter and phenomena are not completely understood and their properties, and potential applications in technology, are still being explored.In this dissertation I will review three selected works involving the application of a new optical magnetic resonance spectroscopy (ODMR) method on ferrimagnetic thin films and in-elastic x-ray spectroscopy at the Advanced Photon Source (APS) that was used to study the correlated f-electron superconductor UTe2 at large hydrostatic pressure up to 52 GPa. This dissertation will then describe the on-going projects to extend NV ODMR spectroscopy to high pressure experiments in search of emergent phases and phenomena such as superconductivity, magnetism, topological insulating states, valence fluctuations, heavy fermion phenomena, and quantum criticality in f-electron materials. First, I will describe research conducted using a new type of ODMR method using nitrogen vacancies (NV) defects in diamond to detect thermal magnons in ferrimagnetic thin films and thin film disks of yttrium iron garnet (YIG). This research demonstrated the detection sensitivity of NVs to a broad range of magnon wavevectors (k) in YIG, up to 5.1 × 107 m-1, as well as observation of parametrically excited magnons and quantized magnon wave modes in patterned disks with radius of 5 μm of 100 nm thin film YIG. A second follow up study used single NV centers to probe changes in the perpendicular magnetic anisotropy (PMA) in thin film YIG. By detecting variations in the single NV relaxation rate, Γ, we were able to extract the effective magnetization 4πM_eff in 8 nm and 12 nm YIG to be -442±7 Oe and -1470±12 Oe, which matches results gathered by traditional ferromagnetic resonance spectroscopy techniques. The spinwave stiffness constant D_s was found to be 8.458×10^(-40) J m^2. This study was followed by research into the structural and electronic properties of UTe2, a novel f- electron superconductor involving resonant x-ray emission spectroscopy (RXES), partial fluorescence yield x-ray absorption spectroscopy (PFY-XAS), and x-ray diffraction experiments (XRD) on UTe2 at high pressure using diamond anvil cells (DACs), at the Argonne National Laboratory’s’ Advanced Photon Source, in search of quantum phase transitions in UTe2 under hydrostatic pressure. High pressure XRD measurements on single crystal UTe2 at room temperature resulted in the discovery of a crystal phase transition in UTe2 from an orthorhombic Immm ordered phase to a tetragonal I4/mmm ordered phase at ~ 7 GPa. Additionally, through a combination of RXES and PFY-XAS we were able to detect a pressure induced change in the U valence from U 3+ to U 4+ at low pressure which then stabilized towards a valence of U 3+ up to 52 GPa.