Understanding the Iterative Polyketide Synthase Involved in Fungal Strobilurin Biosynthesis
Final Report Abstract
Strobilurins are potent antifungal agents that are themselves produced by fungi. They form the basis for the very successful and widely used QoI family of agricultural fungicides that underpin food security worldwide. Our past work elucidated how strobilurins are biosynthesised at the genetic and biochemical levels. In short, a polyketide synthase (PKS) enzyme creates the carbon skeleton of the strobilurins by acting as a highly-programmed synthesis machine. Then a series of so-called tailoring enzymes modify the skeleton to give it its potent bioactive properties. Our initial work showed that the PKS had a well defined and very unusual synthesis programme. At the time this could not be understood, but we realised that the strobilurin system would form an excellent model system that could enable better understanding of PKS in general. In-turn this could eventually allow us to engineer the PKS enzymes to synthesise new compounds to programems specified by humans rather than nature. Such programmed biological synthetic systems will have key roles in the sustainable production of complex molecules after the phaseout of oil-based production systems. Thus our aim was to understand how the strobilurin PKS is programmed. Our strategy involved separating the multifunctional strobilurin PKS into indivdual enzyme components that could be studied in isolation. In parallel with this we synthesised almost every possible chemical intermediate on the strobilurin pathway. We then tested the separate enzymes and chemical substrates in isolation, and used sensitive chemical detection methods to determine the chemical products in each case. This has allowed us to unpick the programme of the strobilurin PKS in very fine detail. We now understand exactly how the PKS controls the programme and at which stage key 'decisions' are made by the protein. Although many of the separate proteins were active in our experiments and we could observe very clear chemical results, we were not able to obtain structural information on the proteins themselves. Knowledge of structure will be key to understanding the precise molecular mechanisms of the decision-making processes. We have therefore begun new collaborative projects with groups who are expert in PKS structural biology and this will form the basis for the next phase of the project.
Publications
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Engineering Aspergillus oryzae for the Heterologous Expression of a Bacterial Modular Polyketide Synthase. Journal of Fungi, 7(12), 1085.
Feng, Jin; Hauser, Maurice; Cox, Russell J. & Skellam, Elizabeth
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Total Mycosynthesis: Rational Bioconstruction and Bioengineering of Fungal Natural Products. Synthesis, 53(14), 2381-2394.
Kahlert, Lukas; Schotte, Carsten & Cox, Russell J.
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Curiouser and curiouser: progress in understanding the programming of iterative highly-reducing polyketide synthases. Natural Product Reports, 40(1), 9-27.
Cox, Russell J.
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Engineered and total biosynthesis of fungal specialized metabolites. Nature Reviews Chemistry, 8(1), 61-78.
Cox, Russell J.
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Comparing total chemical synthesis and total biosynthesis routes to fungal specialized metabolites. Natural Product Reports, 42(4), 720-738.
Tian, Dong-Song; Zhang, Xiao & Cox, Russell J.
