Biomedical Engineering
University of Utah
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The research projects in the Molecular Bioengineering Lab share a couple common threads. The first is adhesion. Projects range from precise molecular adhesion of proteins with defined orientations on activity preserving interfaces to bulk adhesives with controlled setting mechanisms for bonding solid materials. The second is tyrosine. The redox activity of tyrosine has been exploited to crosslink proteins and polymers through homocoupling of tyrosine free radicals, for electrochemical deposition of tyrosine copolymers on electrodes, and crosslinking of copolymers containing the hydroxylated tyrosine derivative, dopa (3,4-dihydroxyphenylalanine). In one way or another the materials that interest us come from nature, either directly as genetically engineered proteins, or as synthetic polymers that mimick natural materials, and sometimes as combinations of both. The sandcastle glue of P. californica P. californica's remarkable underwater adhesive is a water-born composition of several proteins and divalent cations (Mg and Ca). One of the key components contributing to interfacial adhesion and covalent curing or hardening of the glue are dopa residues scattered throughout the glue proleins. The setting reaction, which occurs within 30 sec, is probably triggered by the pH change that occurs when the glue is secreted into seawater. Current research goals include identification of additional protein components, understanding the role of the metal ions, and studying the biological processing that may contribute to the glue's structure, adhesive properties, and setting mechanism. Synthetic mimics of the P. californica bioadhesive Investigation of the structure, composition, and bonding mechanisms of the natural adhesive has provided a foundation for a unique approach to developing new water-based bulk adhesives with controlled setting mechanisms. Key features of the natural adhesive, including the dopa functionality, have been copied into synthetic polymeric adhesives that are being tested for repairing bone fractures. Tyrosine chemistry Tyrosine has a broad range of biological functions because of the unique redox properties of its phenolic sidechain. Tyrosine is one of the few natural amino acids that can exist as a stable free radical. An important natural tyrosine function is protein crosslinking. Natural tyrosine crosslinking is catalyzed by a diverse group of metalloenzymes and through several distinct chemical mechanisms. One route is direct homocoupling of tyrosine free radicals. A second route is enzymatic oxidation of tyrosine to dihydroxyphenylalanine (dopa), which upon further oxidation to dopaquinone readily reacts with nucleophilic groups. We have developed methods to exploit the unique redox properties of tyrosine for protein crosslinking and surface modification that are described briefly on the next page. |
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