Note to users. If you're seeing this message, it means that your browser cannot find this page's style/presentation instructions -- or possibly that you are using a browser that does not support current Web standards. Find out more about why this message is appearing, and what you can do to make your experience of our site the best it can be.

Science 9 November 2007:
Vol. 318. no. 5852, pp. 970 - 974
DOI: 10.1126/science.1148790
Prev | Table of Contents | Next

Reports

GNAT-Like Strategy for Polyketide Chain Initiation

Liangcai Gu,1,2* Todd W. Geders,1,6* Bo Wang,4 William H. Gerwick,7 Kristina Håkansson,4 Janet L. Smith,1,3{dagger} David H. Sherman1,2,4,5{dagger}

An unexpected biochemical strategy for chain initiation is described for the loading module of the polyketide synthase of curacin A, an anticancer lead derived from the marine cyanobacterium Lyngbya majuscula. A central GCN5-related N-acetyltransferase (GNAT) domain bears bifunctional decarboxylase/S-acetyltransferase activity, both unprecedented for the GNAT superfamily. A CurA loading tridomain, consisting of an adaptor domain, the GNAT domain, and an acyl carrier protein, was assessed biochemically, revealing that a domain showing homology to GNAT (GNATL) catalyzes (i) decarboxylation of malonyl-coenzyme A (malonyl-CoA) to acetyl-CoA and (ii) direct S-acetyl transfer from acetyl-CoA to load an adjacent acyl carrier protein domain (ACPL). Moreover, the N-terminal adapter domain was shown to facilitate acetyl-group transfer. Crystal structures of GNATL were solved at 1.95 angstroms (ligand-free form) and 2.75 angstroms (acyl-CoA complex), showing distinct substrate tunnels for acyl-CoA and holo-ACPL binding. Modeling and site-directed mutagenesis experiments demonstrated that histidine-389 and threonine-355, at the convergence of the CoA and ACP tunnels, participate in malonyl-CoA decarboxylation but not in acetyl-group transfer. Decarboxylation precedes acetyl-group transfer, leading to acetyl-ACPL as the key curacin A starter unit.

1 Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA.
2 Department of Medicinal Chemistry, University of Michigan, Ann Arbor, MI 48109, USA.
3 Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109, USA.
4 Department of Chemistry, University of Michigan, Ann Arbor, MI48109, USA.
5 Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI 48109, USA.
6 Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA.
7 Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA92093, USA.

* These authors contributed equally to this work.

{dagger} To whom correspondence should be addressed. E-mail: davidhs{at}umich.edu (D.H.S.); JanetSmith{at}umich.edu (J.L.S.)

Read the Full Text


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Phylogenetic and Chemical Diversity of Three Chemotypes of Bloom-Forming Lyngbya Species (Cyanobacteria: Oscillatoriales) from Reefs of Southeastern Florida.
K. Sharp, K. E. Arthur, L. Gu, C. Ross, G. Harrison, S. P. Gunasekera, T. Meickle, S. Matthew, H. Luesch, R. W. Thacker, et al. (2009)
Appl. Envir. Microbiol. 75, 2879-2888
   Abstract »    Full Text »    PDF »
Isolation and Identification of Rhizoxin Analogs from Pseudomonas fluorescens Pf-5 by Using a Genomic Mining Strategy.
J. E. Loper, M. D. Henkels, B. T. Shaffer, F. A. Valeriote, and H. Gross (2008)
Appl. Envir. Microbiol. 74, 3085-3093
   Abstract »    Full Text »    PDF »
Crystal Structure of the ECH2 Catalytic Domain of CurF from Lyngbya majuscula: INSIGHTS INTO A DECARBOXYLASE INVOLVED IN POLYKETIDE CHAIN -BRANCHING.
T. W. Geders, L. Gu, J. C. Mowers, H. Liu, W. H. Gerwick, K. Hakansson, D. H. Sherman, and J. L. Smith (2007)
J. Biol. Chem. 282, 35954-35963
   Abstract »    Full Text »    PDF »


To Advertise     Find Products

Science. ISSN 0036-8075 (print), 1095-9203 (online)