Doctor of Philosophy (PhD)
This dissertation summarizes the recent findings on complex biomacromolecules in cell wall of plants and fungi which perform important roles in cell recognition, structural build up, and energy storage. Because of the technical difficulty in characterizing these biomacromolecules, which are often polymorphic and disordered in structure, the functional structure of these biomacromolecules remains elusive. In this dissertation, I present two solid-state nuclear magnetic resonance (ssNMR) and dynamic nuclear polarization (DNP) studies of carbohydrate-rich biosystems: the energy-rich plant biomass and disease-relevant, pathogenic fungi.
First, we have investigated the secondary cell wall of plant biomass which is a carbohydrate-rich biosystem using solid state nuclear magnetic resonance spectroscopy. In the intact stems of energy crops, such as switchgrass and maize, lignin self-aggregates to create hydrophobic nanodomains, which are connected to cellulose microfibrils via broad xylan interfaces. Through electrostatic interactions, non-flat xylan conformers bind the intrinsically disordered aromatics of lignin, whereas flat conformers bind the cellulose microfibrils surface. In woods, lignin principally packs with the xylan in a non-flat conformation via non-covalent interactions and partially binds the junction of flat-ribbon xylan and cellulose surface as a secondary site. All molecules are homogeneously mixed in softwoods; this unique feature enables water retention even around the hydrophobic aromatics. These findings shed light on into the functional structure of polysaccharides, their interaction with other biomolecules such as lignin and proteins, and the molecular architecture structure of cell walls. Additionally, the statistical analysis and structural elucidation of unlabeled biomacromolecules using DNP is discussed. Indeed, DNP is frequently used to overcome sensitivity limitations and to examine the intermolecular interface interactions.
Second, we studied the fungal cell walls of a major pathogen Aspergillus fumigatus and found it to contain a hydrophobic frame of α-1,3-glucan, and chitin, which is encased in a hydrated model of diversely connected glucans and, glycoprotein-rich outer layer. These findings created the first high-resolution model of fungal cell walls using ssNMR, allowing for in-cell, high-resolution drug impact characterization to aid in the development of antifungals that target fungal cell walls.
Kirui, Alex Kipchirchir, "Functional Structure of Biomacromolecules in Plant Biomass Using Solid-State NMR and Dynamic Nuclear Polarization" (2021). LSU Doctoral Dissertations. 5732.