[Zurück]

F. Rudroff:
"Catalytic Cascades - `En Route´ to Applied Biochemical Cell-Factories";
TU Wien / Technische Chemie, 2018.

An immense number of chemical reactions is carried out simultaneously in living cells. Nature's optimization approach encompasses the assembly of reactions in cascades and embeds them in finely tuned metabolic networks. Multistep cascades in living organisms commonly function without separation of intermediates; concentrations of all reactants are kept low, which allows high selectivity and avoids by-product formation. Taking Nature as a model, application of cascade reactions in organic synthesis offers a lot of advantages over the classical step-by-step approach. As there is no need for purification of intermediates, operating time, costs and waste are reduced; atom economy and overall yields are improved. Moreover, problems of unstable or toxic intermediates can be overcome and cooperative effects of multiple catalysts can shift reaction equilibria to increase overall cascade productivity (Figure 1).
Enzymes can be used as catalytic platforms for the transformation of functional groups in organic synthesis. Exploiting the manifoldness of enzymes and their different catalytic activities, we envisaged investigating a `general concept´ for the introduction of multi-enzyme reactions in living cells. The design of such new biosynthetic pathways is based on a classical `retrosynthetic´ approach. This technique is used in the strategic planning of organic syntheses by transforming a target molecule into simpler precursors whereas molecular complexity is reduced by manipulation of functional groups. The power of retrosynthetic analysis becomes evident in the design of a synthesis.
We designed de novo pathways of `non´ related enzymes and introduced them into the well-established model organism Escherichia coli. These `artificial mini pathways´ are constructed by enzymes according to their functional group transformations of a particular class of substrates. Thereby we exploited their substrate promiscuity and inherently high chemo-, regio-, and enantioselectivity. The combination of strategies and concepts from organic chemistry, biocatalysis, metabolic engineering and synthetic biology led to the development of such artificial metabolic pathways displaying minimized interference with the cellular host environment, optimized carbon flux through the cell and increased product yields.