Publication Date:
2007-11-10
Description:
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 (GNAT(L)) 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 (ACP(L)). Moreover, the N-terminal adapter domain was shown to facilitate acetyl-group transfer. Crystal structures of GNAT(L) 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-ACP(L) 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-ACP(L) as the key curacin A starter unit.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gu, Liangcai -- Geders, Todd W -- Wang, Bo -- Gerwick, William H -- Hakansson, Kristina -- Smith, Janet L -- Sherman, David H -- DK42303/DK/NIDDK NIH HHS/ -- GM076477/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2007 Nov 9;318(5852):970-4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17991863" target="_blank"〉PubMed〈/a〉
Keywords:
Acetyl Coenzyme A/metabolism
;
Acetyltransferases/*chemistry/*metabolism
;
Acyl Carrier Protein/chemistry/metabolism
;
Amino Acid Sequence
;
Carboxy-Lyases/chemistry/metabolism
;
Crystallography, X-Ray
;
Cyanobacteria/*enzymology/genetics
;
Cyclopropanes/*metabolism
;
Decarboxylation
;
Malonyl Coenzyme A/metabolism
;
Models, Molecular
;
Molecular Sequence Data
;
Polyketide Synthases/*chemistry/genetics/*metabolism
;
Protein Conformation
;
Protein Structure, Tertiary
;
Thiazoles/*metabolism
Print ISSN:
0036-8075
Electronic ISSN:
1095-9203
Topics:
Biology
,
Chemistry and Pharmacology
,
Computer Science
,
Medicine
,
Natural Sciences in General
,
Physics
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