Theses and Dissertations

ORCID

https://orcid.org/0000-0003-3320-4336

Issuing Body

Mississippi State University

Advisor

Fitzkee, Nicholas C

Committee Member

Park, Joo Youn

Committee Member

Emerson, Joseph P

Committee Member

Johnson, Christopher N

Committee Member

Mlsna, Todd E

Date of Degree

12-8-2023

Document Type

Dissertation - Open Access

Major

Chemistry

Degree Name

Doctor of Philosophy (Ph.D)

College

College of Arts and Sciences

Department

Department of Chemistry

Abstract

Biofilms formed on medical devices pose significant challenges, compromising device efficiency and serving as sources of infection. Staphylococcus epidermidis, an opportunistic pathogen, relies on the autolysin protein, notably its R2ab and amidase domains, to attach to polystyrene surfaces and initiate biofilm formation. Despite their pivotal role, the structural intricacies of these proteins’ interactions with surfaces remain elusive. In this dissertation, the multifaceted aspects of protein interactions with polystyrene surfaces and the implications of these interactions for biofilm control are studied. Over the course of this study, it is found how the R2ab and amidase domains influence biofilm formation on polystyrene surfaces. Pretreatment of polystyrene plates with these domains effectively inhibits biofilm growth, underscoring their strong affinity for polystyrene surfaces. Furthermore, these domains demonstrate a remarkable propensity for interactions with polystyrene nanoparticles (PSNPs). The insights gained from this study offer promising avenues for the development of novel biofilm eradication strategies, with the potential to enhance the longevity and effectiveness of medical devices. Shifting to a broader context of nanotechnology, the influence of nanoparticle size on protein adsorption and unfolding stabilities is studied using two distinct proteins, R2ab and GB3. Isothermal titration calorimetry reveals tighter binding to smaller PSNPs for both proteins, with enthalpy as the driving force. Structural changes in the adsorbed proteins are detected through fluorescence spectroscopy and circular dichroism, indicating a propensity for protein unfolding upon adsorption. Importantly, this unfolding effect is less pronounced with larger PSNPs, which has implications for protein binding on macroscopic surfaces. The significance of side-on interactions between neighboring proteins is underscored in this work, since they appear to stabilize proteins bound to surfaces with low curvature, an observation with critical implications for the protein corona formed around nanoparticles and its potential to preserve the structure of surface-adsorbed proteins in vivo. This dissertation also investigates the molecular-level interaction between R2ab and PSNPs of varying sizes. By utilizing lysine methylation in mass spectrometry and hydrogen-deuterium exchange (HDX) NMR spectroscopy, this work investigates how changes in methylation patterns and hydrogen-deuterium exchange rates in specific regions of R2ab reflect conformational changes upon binding to PSNPs. In conclusion, this dissertation comprehensively explores protein-surface interactions and reveals several important and surprising features of the proteins that drive biofilm formation.

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