Characterization and Functionalization of Suckerin-12 Protein Hydrogels

Date of Award

2018

Degree Name

Ph.D. in Engineering

Department

Department of Chemical, Materials and Bioengineering

Advisor/Chair

Advisor: Kristen Comfort

Abstract

Previous research of suckerin proteins identified in the sucker ring teeth of cephalopods have impressive mechanical properties and behave as thermoplastic materials. In this research, one isoform of suckerin protein, suckerin-12 was explored as a mechanically robust material. The protein was isolated and recombinantly expressed in E. coli. Gram-scale quantities of pure protein were expressed and purified to create enzymatically crosslinked hydrogels. Exposure to select salt anion conditions caused the hydrogels to contract significantly, at rates highly dependent upon the anion present in the buffer, which followed a trend modeled by the Hofmeister Series of anions. Mechanical properties of the condensed material were also found to be anion specific. However, the observed changes in hydrogel mechanical properties were best explained by the ability of the salt to neutralize charges in suckerin-12 by deprotonation or charge screening of histidine residues, which are plentiful in the suckerin-12 protein (8 mol%). Thus, by changing the anions in the condensing salt solution, it is possible to tune the mechanical properties of suckerin-12 hydrogels. In addition to anion responsive properties, suckerin-12 hydrogels were discovered to exhibit the same order of magnitude of mechanical properties at both 3 wt% and 6 wt% protein concentrations. However, the final condensed size for 3 % samples is smaller than 6 %. This observation could suggest a mechanism of concentration gradient for the creation of teeth in the native ring tooth structure.In addition to the characterization of mechanical properties associated with suckerin-12 protein hydrogels, this dissertation dually focused on assessing a route for enzyme stabilization utilizing suckerin-12 as the protein matrix. The condensed protein hydrogels were hypothesized to exhibit protection via low water content, beta-sheet secondary structure, and potential molecular crowding mechanisms. Simple adsorption of enzyme in these protein hydrogels proved unsuccessful, as diffusion limited the protection. Many iterations of chemical conjugation molecules were created that tethered the enzyme of choice to suckerin-12 protein. The most successful conjugation method utilized Spy Tag/Catcher chemistry where the enzyme was covalently attached to GFP, a hydrophobic beta-barrel protein that was also discovered in this research to bind non-specifically and tightly to suckerin-12 hydrogels. Having demonstrated successful spy chemistry, this research will allow for the functionalization of suckerin-12 hydrogels with enzymes, nanoparticles, drug and pharmaceutical related small molecules, and even antibodies.

Keywords

Materials Science, Suckerin, Protein Hydrogels, Suckerin-12

Rights Statement

Copyright © 2018, author

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