1gar
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(New page: 200px<br /><applet load="1gar" size="450" color="white" frame="true" align="right" spinBox="true" caption="1gar, resolution 1.96Å" /> '''TOWARDS STRUCTURE-BA...)
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TOWARDS STRUCTURE-BASED DRUG DESIGN: CRYSTAL STRUCTURE OF A MULTISUBSTRATE ADDUCT COMPLEX OF GLYCINAMIDE RIBONUCLEOTIDE TRANSFORMYLASE AT 1.96 ANGSTROMS RESOLUTION
Overview
An inhibitor complex structure of glycinamide ribonucleotide, transformylase (GAR-Tfase; EC 2.1.2.2) from Escherichia coli has been, determined with a multisubstrate adduct BW1476U89 to an R-value of 19.1%, at 1.96 A resolution. The structure was determined by a combination of, molecular and single isomorphous replacement using data from two different, monoclinic crystal lattices and collecting data from crystals soaked in, 20% (w/v) methyl-pentanediol as cryoprotectant for shock-freezing at -150, degrees C. The multisubstrate adduct is bound in an extended crevice at, the interface between the two functional domains of the enzyme. This, inhibitor is positioned in the binding site by three sets of tight, interactions with its phosphate, glutamate and pyrimidone ring moieties, while its interventing linker atoms are more flexible and adopt two, distinct sets of conformations. The highly conserved Arg103, His108 and, Gln170 residues that are key in ligand binding and catalysis (His108), have compensatory conformational variation that gives some clues as to, their role in substrate specificity and in the formyl transfer. The, molecular design of 1476U89 as a multisubstrate adduct inhibitor (Ki, approximately 100 pM at pH 8.5), is confirmed as it closely mimics the, shape, molecular interaction and combined binding constants of the natural, 10-formyltetrahydrofolate (10-CHO-H4F; Km approximately 77.4 microM at pH, 8.5) and glycinamide-ribonucleotide (GAR; Km approximately 8.1 microM at, pH 8.5) substrates. The stereochemistry of this ligand complex suggests, that His108 may act as an electrophile stabilizing the oxyanion of the, tetrahedral intermediate that is formed as a result of the direct attack, on the 10-CHO-H4F by the amino group of GAR. Structural comparison of the, folate binding modes among GAR-Tfase, dihydrofolate reductase and, thymidylate synthase reveals that folate derivates bound to GAR-Tfase, differentially adopt the trans conformation for the dihedral angle between, atoms C-6 and C-9 providing a handle for targeting specific, folate-dependent enzymes. The structural information derived from two, different discrete conformations of the ligand in the binding site also, suggests several leads for the de novo design of inhibitors of GAR-Tfase, that may develop into useful chemotherapeutic agents.
About this Structure
1GAR is a Single protein structure of sequence from Escherichia coli with U89 as ligand. Active as Phosphoribosylglycinamide formyltransferase, with EC number 2.1.2.2 Full crystallographic information is available from OCA.
Reference
Towards structure-based drug design: crystal structure of a multisubstrate adduct complex of glycinamide ribonucleotide transformylase at 1.96 A resolution., Klein C, Chen P, Arevalo JH, Stura EA, Marolewski A, Warren MS, Benkovic SJ, Wilson IA, J Mol Biol. 1995 May 26;249(1):153-75. PMID:7776369
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