1QR7: Crystal Structure of Phenylalanine-regulated 3-deoxy-d- Arabino-heptulosonate-7-phosphate Synthase From Escherichia Coli Complexed With Pb2+ and PEP

Citation:
Abstract
BACKGROUND: In microorganisms and plants the first step in the common pathway leading to the biosynthesis of aromatic compounds is the stereospecific condensation of phosphoenolpyruvate (PEP) and D-erythrose-4-phosphate (E4P) giving rise to 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP). This reaction is catalyzed by DAHP synthase (DAHPS), a metal-activated enzyme, which in microorganisms is the target for negative-feedback regulation by pathway intermediates or by end products. In Escherichia coli there are three DAHPS isoforms, each specifically inhibited by one of the three aromatic amino acids. RESULTS: The crystal structure of the phenylalanine-regulated form of DAHPS complexed with PEP and Pb2+ (DAHPS(Phe)-PEP-Pb) was determined by multiple wavelength anomalous dispersion phasing utilizing the anomalous scattering of Pb2+. The tetramer consists of two tight dimers. The monomers of the tight dimer are coupled by extensive interactions including a pair of three-stranded, intersubunit beta sheets. The monomer (350 residues) is a (beta/alpha)8 barrel with several additional beta strands and alpha helices. The PEP and Pb2+ are at the C-ends of the beta strands of the barrel, as is SO4(2-), inferred to occupy the position of the phosphate of E4P. Mutations that reduce feedback inhibition cluster about a cavity near the twofold axis of the tight dimer and are centered approximately 15 A from the active site, indicating the location of a separate regulatory site. CONCLUSIONS: The crystal structure of DAHPS(Phe)-PEP-Pb reveals the active site of this key enzyme of aromatic biosynthesis and indicates the probable site of inhibitor binding. This is the first reported structure of a DAHPS; the structure of its two paralogs and of a variety of orthologs should now be readily determined by molecular replacement.
PDB ID: 1QR7Download
MMDB ID: 11259
PDB Deposition Date: 1999/6/18
Updated in MMDB: 2007/10 
Experimental Method:
x-ray diffraction
Resolution: 2.6  Å
Source Organism:
Similar Structures:
Biological Unit for 1QR7: tetrameric; determined by author and by software (PISA)
Molecular Components in 1QR7
Label Count Molecule
Proteins (4 molecules)
4
Phenylalanine-regulated 3-deoxy-d-arabino- Heptulosonate-7-phosphate Synthase
Molecule annotation
Chemicals (12 molecules)
1
4
2
4
3
4
* Click molecule labels to explore molecular sequence information.

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