Bionic alkyltransferases for biocatalysis

Biocatalysis, an emerging green technology, has demonstrated its efficacy from bench-scale experimentation to industrial applications. Harnessing understanding of enzymes derived from natural sources, most research activity in biocatalysis focuses on the optimization of enzymes via directed evolution and computational design. Recent advancements in protein engineering have highlighted significant breakthroughs, including repurposing the natural catalytic activities to desired activities and broadening the substrate scopes. The potential of biocatalysis may also lie in the development of enzyme-catalyzed processes that are not occurring in nature but enables entirely novel biocatalytic strategies. This thesis focuses on one such approach and applies it in fluorine chemistry.
Fluorine has found diverse applications in everyday products, such as toothpastes, water- and oil-repellent containers to pharmaceutical products. Large demand for fluorinated products has spurred long-standing history of organofluorine synthesis. Despite a rich history of organofluorine synthesis, naturally occurring fluorinated compounds are scarce, with fluorinase being the only known fluorinating enzyme in nature.
This thesis presents the utilization of methyltransferases and halide methyltransferase in the synthesis of fluoromethylated products, encompassing N, C, O nucleophiles, from small molecule substrates to proteins. The enzyme-catalyzed fluoromethylation extends its application to ligations between small molecules, peptides and proteins labelling, as well as protein synthesis.
While fluorinated compounds have diverse applications, they pose environmental challenge as “forever chemicals” that become health hazards for both human and animals. Selenium, accumulating due to manufacturing activities, shares a similar environmental impact. Some plants have evolved the ability to mitigate selenium levels through the volatilization of Se, possibly in the form of dimethyl selenide. The enzymes that facilitate this process are poorly understood.
Part of this thesis contributes to the understanding of sulfur and selenium volatilization by detailing the biochemical activity and structural characterization of an enzyme, dimethyl sulfide synthase, which potentially regulates the selenium/sulfur level in microbes. The plant homologs of this enzyme may play a role in selenium volatilization, contributing to phytodetoxification processes.
This thesis sheds light on novel biocatalytic reactions in fluorine chemistry and selenium volatization, with an emphasis on sensible molecular design and degradation processes.