Deconstructing Aflatoxin B1 Production

Craig A. Townsend, Ph.D.
Department of Chemistry, Johns Hopkins University
NIEHS Grant R01ES001670

NIEHS grantees describe the function of polyketide synthases, enzymes involved in the synthesis of the fungal product and human carcinogen aflatoxin B1, in a paper in the April 11 issue of Science. Understanding this process and the specificity of the chemical structures created by the enzymes may lead to redesigning the enzymes for the synthesis of new molecules and drugs.

Polyketides comprise a diverse range of naturally occurring compounds with a high degree of variability in biological activities and pharmacological properties. The team used the Udwary-Merski bioinformatics algorithm to dissect one polyketide synthase known as PksA into its various domains. They then recombined the constructs in vitro and analyzed the products that were formed. Their goal was to identify the domains that control polyketide chain length, cyclization of the intermediate products, and product release.

The team identified the specific domains that elongate the polyketide chain to a fixed length, drive the cyclization of the first two ring structures in aflatoxin and finally the domain that controls cyclization of the third ring and also mediates the release of the product. The researchers conclude that the mechanistic features they identified here should apply to catalysis in general and that the insights provided by this dissection approach enable a rational strategy for engineering these enzymes to synthesize alternative products.

Citation: Crawford JM, Thomas PM, Scheerer JR, Vagstad AL, Kelleher NL, Townsend CA. Deconstruction of iterative multidomain polyketide synthase function. Science. 2008 Apr 11;320(5873):243-6.