This polyketide synthase, characterized from the bacteria Streptomyces orinoci and Streptomyces spectabilis, generates the backbone of the antibiotic spectinabilin. It is composed of 6 modules that total 28 domains and is encoded by four genes. The enzyme accepts the unusual starter unit 4-nitrobenzoyl-CoA and extends it by 6 molecules of (S)-methylmalonyl-CoA and a single molecule of malonyl-CoA. The first module (encoded by norA) is used twice in an iterative fashion, so that the seven Claisen condensation reactions are catalysed by only six modules. The iteration becomes possible by the transfer of the [acp]-bound polyketide intermediate back to the ketosynthase (KS) domain on the opposite polyketide synthase strand (polyketides are homodimeric).
The expected taxonomic range for this enzyme is: Streptomyces
This polyketide synthase, characterized from the bacteria Streptomyces orinoci and Streptomyces spectabilis, generates the backbone of the antibiotic spectinabilin. It is composed of 6 modules that total 28 domains and is encoded by four genes. The enzyme accepts the unusual starter unit 4-nitrobenzoyl-CoA and extends it by 6 molecules of (S)-methylmalonyl-CoA and a single molecule of malonyl-CoA. The first module (encoded by norA) is used twice in an iterative fashion, so that the seven Claisen condensation reactions are catalysed by only six modules. The iteration becomes possible by the transfer of the [acp]-bound polyketide intermediate back to the ketosynthase (KS) domain on the opposite polyketide synthase strand (polyketides are homodimeric).
enzyme generates the backbone of the antibiotic spectinabilin. It is composed of 6 modules and is encoded by four genes. The enzyme extends 4-nitrobenzoyl-CoA by 6 molecules of (S)-methylmalonyl-CoA and a single molecule of malonyl-CoA. The first module (encoded by norA) is used twice in an iterative fashion, so that the seven Claisen condensation reactions are catalysed by only six modules. The iteration becomes possible by the transfer of the [acp]-bound polyketide intermediate back to the ketosynthase (KS) domain on the opposite polyketide synthase strand (polyketides are homodimeric). Comparison of Stretomyces thiolueus aureothin and Streptomyces orinoci neoaureothin gene clusters and enzymes
the polyketidsynthase system consists of 4 subunits. SpnA is an iterative modular type I polyketide synthase. Six PKS modules of the spectinabilin cluster catalyze seven rounds of elongation and reduction. SpnA' is a biomodular protein of the same domain architecture of SpnA (ketosynthase, acyl transferase, dehydratase, ketoreductase and acyl carrier protein), which is responsible for two successive unsaturated chain elongation steps using methylmalonyl-CoA. SpnB contains a sequence of malonyl-CoA specificity in the AT domain, which leads to a full reduction of the beta-keto group after condensation of malonyl-coA.7 SpnC carries two modules of ketosynthase, acyl transferase, and acyl carrier protein domains and a C-terminal thioesterase domain and catalyzes the last two Claisen condensations
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