1tmj

File:1tmj.gif

spinqualitylabelsall models 1tmj, resolution 1.45Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Crystal structure of E.coli apo-HPPK(W89A) at 1.45 Angstrom resolution

OverviewOverview

Deletion mutagenesis, biochemical, and X-ray crystallographic studies have, shown that loop 3 of Escherichia coli 6-hydroxymethyl-7,8-dihydropterin, pyrophosphokinase (HPPK) is required for the assembly of the active, center, plays an important role in the stabilization of the ternary, complex of HPPK with MgATP and 6-hydroxymethyl-7,8-dihydropterin (HP), and, is essential for catalysis. Whether the critical functional importance of, loop 3 is due to the interactions between residues R84 and W89 and the two, substrates has been addressed by site-directed mutagenesis, biochemical, and X-ray crystallographic studies. Substitution of R84 with alanine, causes little changes in the dissociation constants and kinetic constants, of the HPPK-catalyzed reaction, indicating that R84 is not important for, either substrate binding or catalysis. Substitution of W89 with alanine, increases the K(d) for the binding of MgATP by a factor of 3, whereas the, K(d) for HP increases by a factor of 6, which is due to the increase in, the dissociation rate constant. The W89A mutation decreases the rate, constant for the chemical step of the forward reaction by a factor of 15, and the rate constant for the chemical step of the reverse reaction by a, factor of 25. The biochemical results of the W89A mutation indicate that, W89 contributes somewhat to the binding of HP and more significantly to, the chemical step. The crystal structures of W89A show that W89A has, different conformations in loops 2 and 3, but the critical catalytic, residues are positioned for catalysis. When these results are taken, together, they suggest that the critical functional importance of loop 3, is not due to the interactions of the R84 guanidinium group or the W89, indole ring with the substrates.

About this StructureAbout this Structure

1TMJ is a Single protein structure of sequence from Escherichia coli with MG and CL as ligands. Active as 2-amino-4-hydroxy-6-hydroxymethyldihydropteridine diphosphokinase, with EC number 2.7.6.3 Full crystallographic information is available from OCA.

ReferenceReference

Is the critical role of loop 3 of Escherichia coli 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase in catalysis due to loop-3 residues arginine-84 and tryptophan-89? Site-directed mutagenesis, biochemical, and crystallographic studies., Li Y, Blaszczyk J, Wu Y, Shi G, Ji X, Yan H, Biochemistry. 2005 Jun 21;44(24):8590-9. PMID:15952765

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