engleski

Ablation of a post-polyketide hydroxylase from the oxytetracyline biosynthetic pathway results in novel polyketides with altered chain length

Oxytetracycline (OTC), a polyketide antibiotic, is made by Streptomyces rimosus through the sequential condensation of eight acetate units to a three-carbon starter unit. The otcC gene encodes a C-6-hydroylase that is involved in the late stages of biosynthesis after the polyketide backbone is completed. A recombinant, which was disrupted in the genomic copy of otcC, synthesized at least three novel polyketides of shorter chain lengths (17 and 16 carbons) than OTC (19 carbons). No compound containing a full-length chain was detected in the recombinant culture. This result indicates that the absence of the otcC gene product has a significant effect on the ability of the OTC ‘ minimal PKS’ to make a polyketide product of the usual chain length. A mutant copy of otcC was made by site-directed mutagenesis of three essential glycine codons located within the putative NADPH-binding domain. Expression of the mutant gene in E. coli confirmed that this gene product was catalytically-inactive. When the mutant gene replaced the ablated gene in the chromosome of S. rimosus, the ability to make a 19-carbon backbone was restored, indicating that OtcC is an essential structural partner in the quaternary structure of the synthase complex.

Streptomyces rimosus; oxytetracycline; otcC gene; C-6-hydroylase; novel polyketides

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