Taylored Enzymes
The global health issue that is antibacterial resistance is a growing and ongoing problem for humanity as the development of new antimicrobials is decreasing while bacteria are becoming more resistant to known antibiotics. Derivatization of antibiotics is a strategy that could lead to the production of versions of the already existing antibiotics that have higher inhibitory activity (Okano, Isley, & Boger, 2017). Many antibiotics are enriched with sugars using glycosyltransferases which are enzymes that attach sugars onto specific substrates ("Antibiotics,"). For example, some glycosyltransferases such as GtfA and GtfB are involved in the synthesis pathway of vancomycin, one of the oldest and still actively used antibiotics (Scholar, 2007). In juxtaposition, another group of glycosyltransferases that are well studied as drug design targets is the heptosyltransferases involved in the synthesis of the chains of polysaccharides called lipopolysaccharides (LPS). The LPS chains are embedded in the cellular surface of Gram-negative bacteria and block antibiotics from entering the cell. They serve as another layer of protection for the cells (Cote & Taylor, 2017). Heptosyltransferase enzymes such as Heptosyltransferase I (HepI) and Heptosyltransferase II (HepII) are glycosyltransferases that are involved in the biosynthetic pathway that builds the LPS by transferring a heptose onto a glycolipid. A closer look at these glycosyltransferases (GtfA, GtfB, HepI, HepII) brings up the idea of glyco- diversification, which can be achieved by domain swapping two structurally similar proteins to create a new protein (Gantt, Peltier-Pain, & Thorson, 2011). The objective of this project is to build an enzyme that can perform similar transferase chemistries with different substrates to create a library of molecules that could potentially create new antibiotics generated by enzyme catalysis. This new chimeric protein will be designed by combining the sugar donor domain of one protein onto the substrate recognition domain of another protein. The aim is to design 4 different chimeric proteins with the natural product binding domains of GtfA and GtfB attached to the sugar donor binding domains of Hep I and Hep II. First, this project will entail the synthesis of the chimeric proteins, followed by the functional characterization of these enzymes first by mass spectroscopy and then by UV-Vis coupled kinetic assays. If successful, this project should allow for the generation of new vancomycin family glycopeptide antibiotic derivatives. Circular Dichroism thermal analysis will also be done on the GtfB protein to understand more about its structure, alone, and in the presence of its substrates.