engleski

Molecular biology of polyketide biosynthesis

Streptomyces species and related genera synthesize a large number of secondary metabolites, many of which are biologically-active. Amongst them, polyketides is the largest class. Polyketides are a structurally-diverse family of natural products with a broad range of biological activities. The formation of polyketides is very similar to biosynthesis of long chain fatty acids - both in the enzymatic reactions that take place and the enzyme proteins that are involved. During the last decade many polyketide gene-clusters have been cloned and sequenced. DNA sequencing has shown that the clusters have substantial homology suggesting that they originated from a common ancestor. This similarity has resulted in development of combinatorial biology techniques to create novel chemical entities. Two approaches have been used: targeted manipulation, e.g. disruption and, often, replacement of certain genes involved in the biosynthetic pathway, and the random approach, e.g. 'gene shuffling'. A targeted approach has been used to generate several novel scaffolds by manipulation of the S. rimosus oxytetracycline gene-cluster. Genes encoding ketosynthase, a and b, ketoreductase, cyclase/aromatase and C-6 hydroxylase were disrupted to construct four recombinant strains. Thin-layer-chromatography and high-liquid-pressure-chromatography of extracts from fermentation broths of all four recombinants showed that they produce about 20 potentially novel metabolites of which 12 have been characterised chemically. In this review, data on the disruption and replacement of the otcC gene will be described in more detail.

polyketides; biosynthetic pathway engineering; Streptomyces rimosus; oxytetracycline

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