Biocatalytic Manipulation of Organosilyl Ethers by Silicatein

Abstract

This study focused on the harnessing of recombinant silicatein enzyme for the synthetic manipulation of organosilyl ethers. The organosilyl ethers are compounds that comprises Si-O bonds and applied in organic chemistry as protecting groups for the alcohol functional group, and precursors for siloxane polymer production in the industry incorporated into products such as medical equipment, cosmetics, automobiles, pharmaceuticals etc. However, the production of organosiloxanes depend on chlorosilanes which carry a large environmental footprint, require high energy and harsh catalysts, and produce undesirable by-products (e.g., HCl). Therefore, new methods with better sustainability and selectivity are desirable for the manipulation of these compounds, thus biocatalysis becomes that viable choice. In this research, we used a Strep-tagged silicatein-α (TF-Silα-Strep) protein to catalyze the reactions of these organosilyl ether compounds to investigate the catalytic activity of the protein in the making and cleavage of Si-O bonds. The results obtained for both organosilyl hydrolysis and condensation reactions catalyzed by the TF-Silα-Strep showed that the protein gave measurable activity in both reactions as shown by the kinetic parameters of the enzyme obtained using Michaelis-Menten plots (chapters 2 and 3), and the percentage conversion of the condensation products (chapters 5 and 6) obtained from the reactions. The roles of the enzyme’s active site catalytic residues (serine, histidine, and asparagine) were investigated to ascertain their activity relative to the Wild type enzyme. Site-directed mutagenesis was employed by replacing the catalytic residues with inactive alanine and the result showed that the residues contributed to the catalysis of Silα indicated by the loss of activity observed in the enzyme mutants (chapter 4). Overall, the result of this study is fundamental to the understanding of the competence of TF-Silα-Strep which showed promise as a viable catalyst for Si-O bond transformations.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Lu Shin Wong (Supervisor) & Christopher Blanford (Supervisor)