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Science 11 April 2008:
Vol. 320. no. 5873, pp. 243 - 246
DOI: 10.1126/science.1154711
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Reports

Deconstruction of Iterative Multidomain Polyketide Synthase Function

Jason M. Crawford,1* Paul M. Thomas,2 Jonathan R. Scheerer,1 Anna L. Vagstad,1 Neil L. Kelleher,2{dagger} Craig A. Townsend1{dagger}

PksA, which initiates biosynthesis of the environmental carcinogen aflatoxin B1, is one of the multidomain iterative polyketide synthases (IPKSs), a large, poorly understood family of biosynthetic enzymes. We found that dissection of PksA and its reconstitution from selected sets of domains allows the accumulation and characterization of advanced octaketide intermediates bound to the enzyme, permitting the reactions controlled by individual catalytic domains to be identified. A product template (PT) domain unites with the ketosynthase and thioesterase in this IPKS system to assemble precisely seven malonyl-derived building blocks to a hexanoyl starter unit and mediate a specific cyclization cascade. Because the PT domain is common among nonreducing IPKSs, these mechanistic features should prove to be general for IPKS-catalyzed production of aromatic polyketides.

1 Department of Chemistry, Johns Hopkins University, Baltimore, MD21218, USA.
2 Department of Chemistry, University of Illinois, Urbana, IL 61801, USA.

* Present address: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.

{dagger} To whom correspondence should be addressed. E-mail: ctownsend{at}jhu.edu (C.A.T.); kelleher{at}scs.uiuc.edu (N.L.K.)

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