Isolation of the biosynthetic gene cluster for tautomycetin, a linear polyketide T cell-specific immunomodulator from Streptomyces sp. CK4412.

The bacterial genus Streptomyces has long been appreciated for its ability to produce various kinds of medically important secondary metabolites, such as antibiotics, anti-tumour agents, immunosuppressants and enzyme inhibitors. Tautomycetin (TMC), which is produced by Streptomyces sp. CK4412, is a novel activated T cell-specific immunosuppressive compound with an ester bond linkage between a terminal cyclic anhydride moiety and a linear polyketide chain bearing an unusual terminal alkene. Using a Streptomyces polyketide methylmalonyl-CoA acyltransferase gene as a probe, three overlapping cosmids were isolated from the genomic library of TMC-producing Streptomyces sp. CK4412. Sequence information of an approximately 70 kb contiguous DNA region revealed two multi-modular type I polyketide synthases (PKSs), and 12 additional gene products presumably involved in TMC biosynthesis. The deduced roles for most of the TMC PKS catalytic domains were consistent with the expected functions necessary for TMC chain elongation and processing. In addition, disruption of a putative TMC acyl-CoA transferase gene, located upstream of the PKS gene locus, completely abolished TMC biosynthesis. Taken together, these data provide strong supporting evidence that the cloned gene cluster identified in this study is responsible for TMC biosynthesis in Streptomyces sp. CK4412, and set the stage for detailed genetic and biochemical studies of the biosynthesis of this important metabolite.