Enzymology and engineering of the biosynthesis of polyether antibiotics

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This project seeks to combine the efforts of two established research teams in Cambridge to solve a major outstanding problem in chemistry and biochemistry: the way in which a certain large group of natural antibiotics called polyethers are produced in Nature. Polyethers are antibiotics, whose clinical use has been restricted by their toxicity and by the difficulty of synthesising them or modifying them chemically, but which have been recently discovered (for example) to be highly effective against drug-resistant malarial parasites, a major global health threat. There is therefore great interest in developing new biological ways of synthesising libraries of such molecules to test as the starting point for potentially improved drugs of lower toxicity. We already know that to build up such complex small molecules from the simple building blocks inside bacterial cells requires multiple steps, each one catalysed by an enzyme. Some of these are physically tethered together into massive multienzyme complexes, the most complex biological catalysts so far discovered, but all are orchestrated to provide a smooth cascade or chain of reactions so that nothing is wasted and typically a single end-product is made. The opportunity for this research arises because one of us (PFL) has recently (with BBSRC support) succeeded for the first time in cloning and sequencing not one but four giant gene clusters governing the biosynthesis of four different polyethers; and his group has developed genetic methods to harness an industrial bacterial strain which overproduces one of these polyethers called monensin, so that products accumulate at levels up to 1000-fold higher than from the wild type, making the analysis of even minor products possible. Understanding polyether biosynthesis in molecular detail will require diverse experimental approaches including genetic manipulation of the genes inside the bacterial cells to see in what way the altered blueprint directs the synthesis of an altered end-product; and attempts to reconstitute portions of the catalysis in the test tube using purified enzymes and artificial substrates. We aim not only to provide a new appreciation of how the properties of individual enzymes are modulated when combined into such an integrated system, but also to learn the rules of how to alter the genes, or combine the genes from two or more polyether pathways, so as deliberately to divert the biosynthesis to make new target natural products. Our joint project aims to accelerate the further development of this exciting technology, with its broad potential benefits in the pharmaceutical industry.