Structure and Dynamics of Fungal Cell Walls Using Solid-State Nuclear Magnetic Resonance Spectroscopy

The main objective of this dissertation research is to summarize the most recent findings on complex biomolecules that play crucial roles in the structure and drug resistance of pathogenic fungi\u27s cell walls. The functional structure of these biomacromolecules is still challenging to characterize due to their frequently diverse and disorganized structural characteristics. Here we present the combing of solid state-nuclear magnetic resonance (ssNMR) and dynamic nuclear polarization (DNP) to provide an excellent insight into spatial proximity, site-specific hydration, structural polymorphism, and biomolecule motion, boosting our knowledge of the importance of individual fungal carbohydrates in the cell wall. First, we studied the cell wall of a major pathogen, the fungus Aspergillus fumigatus. We found it to contain rigid hydrophobic scaffolds of chitin and α-glucans, surrounded by a hydrated mobile matrix of β-glucans and capped by a dynamic layer containing mannan and galactan-based polymers as well as glycoproteins. Next, we incorporated multidimensional ssNMR and chemical analysis to understand how the fungal cell wall arrangement is reshuffled in an array of mutants deficient in the biosynthesis of α-1,3-glucan, chitin, galactomannan, and galactosaminogalactan, respectively. Our results show that disruption of the biosynthesis of any polysaccharide will lead to global changes in the molecular composition regarding both the internal and external domains of fungal cell walls. The rebuilt cell walls featured increased polymer stiffness and decreased water retention in the inner domain compared with the parental cell wall that protects cellular integrity and accommodates growth. Second, our focus was on understanding how antifungals interact with different pathogenic fungi that are drug resistant. We found that removing β-1,3-glucan from the cell wall inner domain is compensated by nitrogenated carbohydrates, which decreases water accessibility in more significant amounts, preventing hydrophilic antifungals from entering cells. These results reveal the structural mechanisms adapted by fungal pathogens to resist antifungals, and this understanding can help develop more effective antifungal treatments