Investigating protein-alginate interactions in solution and gel and its effect on protein properties
Chang, Roger
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https://hdl.handle.net/2142/122104
Description
Title
Investigating protein-alginate interactions in solution and gel and its effect on protein properties
Author(s)
Chang, Roger
Issue Date
2023-11-17
Director of Research (if dissertation) or Advisor (if thesis)
Gruebele, Martin
Kong, Hyun Joon
Rogers, Simon A
Doctoral Committee Chair(s)
Leckband, Deborah E
Department of Study
Chemical & Biomolecular Engr
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Alginate
Protein
Abstract
This thesis describes novel investigations of protein folding stability, folding kinetics, and aggregation in alginate solutions and in three-dimensional polymer gels. Polymers designed to stabilize proteins exploit direct protein-polymer interactions or crowding, but how these interactions increase stability or reduce aggregation is rarely established. Proteins are commonly encapsulated in alginate gels for drug delivery and tissue engineering applications. However, there is limited knowledge on how encapsulation impacts the intrinsic protein properties such as folding stability or unfolding kinetics. The impact on protein structure in different microenvironments was monitored based on changes in fluorescence resonance energy transfer (FRET) of the conformation-reporter of Phosphoglycerate Kinase (PGK-FRET), using both static and dynamic fluorescence measurements. Chapter 2 details how soluble alginate affects protein properties such as folding stability, aggregation behavior, and folding reversibility in bulk solutions. Chapter 3 describes studies with fast relaxation imaging and bulk fluorescence measurements to determine how encapsulation in alginate gels alters PGK-FRET folding thermodynamics and kinetics. Findings show that alginate solutions and gels both stabilize PGK. However, encapsulation and associated confinement appear to both stabilize protein folding and accelerate unfolding. Both soluble alginate and alginate gels stabilize proteins, and the stabilization depends non monotonically on the alginate concentration; namely, low alginate concentrations are the most stabilizing, but the effect decreases at higher alginate concentrations. Kinetic measurements of thermally induced protein unfolding in situ reveal that encapsulation accelerates protein unfolding and causes the protein, PGK, to deviate from two state folding behavior. Phi-value analysis of protein unfolding within gels suggests that, in gels, the transition state structure is similar to the folded protein and that alginate encapsulation stabilizes the folded state, relative to the transition state. This work reveals that alginate increases the protein folding stability. In addition, comparisons of protein folding behavior in alginate solutions versus in hydrogels reveal both stabilizing and destabilizing effects of encapsulation. The approaches and findings reported in this thesis can guide the design of hybrid alginate/protein materials to optimize performance and increase
device shelf-life.
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