2gar: Difference between revisions
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==Overview== | ==Overview== | ||
A mutation in the dimer interface of Escherichia coli glycinamide, ribonucleotide transformylase (GarTfase) disrupts the observed, pH-dependent association of the wild-type enzyme, but has no observable, effect on the enzyme activity. Here, we assess whether a pH effect on the, enzyme's conformation is sufficient by itself to explain the pH-dependence, of the GarTfase reaction. A pH-dependent conformational change is observed, between two high-resolution crystal structures of the Glu70Ala mutant, GarTfase at pH 3.5 (1.8 A) and 7.5 (1.9 A). Residues 110 to 131 in, GarTfase undergo a transformation from a disordered loop at pH 3.5, where, the enzyme is inactive, to an ordered loop-helix structure at pH 7.5, where the enzyme is active. The ordering of this flexible loop-helix has a, direct ... | A mutation in the dimer interface of Escherichia coli glycinamide, ribonucleotide transformylase (GarTfase) disrupts the observed, pH-dependent association of the wild-type enzyme, but has no observable, effect on the enzyme activity. Here, we assess whether a pH effect on the, enzyme's conformation is sufficient by itself to explain the pH-dependence, of the GarTfase reaction. A pH-dependent conformational change is observed, between two high-resolution crystal structures of the Glu70Ala mutant, GarTfase at pH 3.5 (1.8 A) and 7.5 (1.9 A). Residues 110 to 131 in, GarTfase undergo a transformation from a disordered loop at pH 3.5, where, the enzyme is inactive, to an ordered loop-helix structure at pH 7.5, where the enzyme is active. The ordering of this flexible loop-helix has a, direct effect on catalytic residues in the active site, binding of the, folate cofactor and shielding of the active site from solvent. A, main-chain carbonyl oxygen atom from Tyr115 in the ordered loop forms a, hydrogen bond with His108, and thereby provides electronic and structural, stabilization of this key active site residue. Kinetic data indicate that, the pKa of His108 is in fact raised to 9. 2. The loop movement can be, correlated with elevation of the His pKa, but with further stabilization, probably from Asp144, after the binding of folate cofactor. Leu118, also, in the loop, becomes positioned near the p-amino benzoic acid binding, site, providing additional hydrophobic interactions with the cofactor, 10-formyl tetrahydrofolate. Thus, the pH-dependence of the enzyme activity, appears to arise from local active site rearrangements and not from, differences due to monomer-dimer association. | ||
==About this Structure== | ==About this Structure== | ||
2GAR is a | 2GAR is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with PO4 as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Phosphoribosylglycinamide_formyltransferase Phosphoribosylglycinamide formyltransferase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.1.2.2 2.1.2.2] Structure known Active Site: E70. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=2GAR OCA]. | ||
==Reference== | ==Reference== | ||
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[[Category: purine biosynthesis]] | [[Category: purine biosynthesis]] | ||
''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on | ''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on Mon Nov 5 12:34:39 2007'' | ||
