2Q2X: Crystal Structure Of The Ech2 Decarboxylase Domain Of Curf From Lyngbya Majuscula

Curacin A is a mixed polyketide/nonribosomal peptide possessing anti-mitotic and anti-proliferative activity. In the biosynthesis of curacin A, the N-terminal domain of the CurF multifunctional protein catalyzes decarboxylation of 3-methylglutaconyl-acyl carrier protein (ACP) to 3-methylcrotonyl-ACP, the postulated precursor of the cyclopropane ring of curacin A. This decarboxylase is encoded within an "HCS cassette" that is used by several other polyketide biosynthetic systems to generate chemical diversity by introduction of a beta-branch functional group to the natural product. The crystal structure of the CurF N-terminal ECH(2) domain establishes that the protein is a crotonase superfamily member. Ala(78) and Gly(118) form an oxyanion hole in the active site that includes only three polar side chains as potential catalytic residues. Site-directed mutagenesis and a biochemical assay established critical functions for His(240) and Lys(86), whereas Tyr(82) was nonessential. A decarboxylation mechanism is proposed in which His(240) serves to stabilize the substrate carboxylate and Lys(86) donates a proton to C-4 of the acyl-ACP enolate intermediate to form the Delta(2) unsaturated isopentenoyl-ACP product. The CurF ECH(2) domain showed a 20-fold selectivity for ACP-over CoA-linked substrates. Specificity for ACP-linked substrates has not been reported for any other crotonase superfamily decarboxylase. Tyr(73) may select against CoA-linked substrates by blocking a contact of Arg(38) with the CoA adenosine 5'-phosphate.
PDB ID: 2Q2XDownload
MMDB ID: 59373
PDB Deposition Date: 2007/5/29
Updated in MMDB: 2017/10
Experimental Method:
x-ray diffraction
Resolution: 2  Å
Source Organism:
Similar Structures:
Biological Unit for 2Q2X: trimeric; determined by author and by software (PISA,PQS)
Molecular Components in 2Q2X
Label Count Molecule
Proteins (3 molecules)
Molecule annotation
Chemicals (6 molecules)
* Click molecule labels to explore molecular sequence information.

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