An antibiotic factory caught in action

Abstract

The synthesis of aromatic polyketides, such as actinorhodin, tetracycline and doxorubicin, begins with the formation of a polyketide chain. In type II polyketide synthases (PKSs), chains are polymerized by the heterodimeric ketosynthase–chain length factor (KS-CLF). Here we present the 2.0-Å structure of the actinorhodin KS-CLF, which shows polyketides being elongated inside an amphipathic tunnel 17 Å in length at the heterodimer interface. The structure resolves many of the questions about the roles of KS and CLF. Although CLF regulates chain length, it does not have an active site; KS must catalyze both chain initiation and elongation. We provide evidence that the first cyclization of the polyketide occurs within the KS-CLF tunnel. The mechanistic details of this central PKS polymerase could guide biosynthetic chemists in designing new pharmaceuticals and polymers.

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Figure 1: Octaketide production by the actinorhodin minimal PKS.
Figure 2: KS-CLF complementarity.
Figure 3: The polyketide tunnel.
Figure 4: Polyketide intermediates.

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Acknowledgements

We thank Y. Tang and S. Kobayashi for valuable conversations about KS-CLF biochemistry and help in transforming into and purifying from S. coelicolor. Research was supported by US National Institutes of Health (NIH) Cancer Institute grants CA 63081 (R.M.S.) and CA 77248 (C.K.). A.T.K. also received a fellowship from the Achievement Rewards for College Scientists Foundation. D.A.M. and K.F.M. were supported by US NIH National Center for Research Resources grants RR 01614 and RR 12961 (to the UCSF MS Facility, director A.L. Burlingame).

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Correspondence to Robert M Stroud.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Fig. 1

KS-CLF secondary structure. (PDF 305 kb)

Supplementary Fig. 2

The proposed CLF active site. (PDF 354 kb)

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