Article of Judit Szabó et al. published in Scientific Reports
|Article of Judit Szabó et al. is published in Scientific Reports
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Members of the dUTPase superfamily play an important role in the maintenance of the pyrimidine nucleotide balance and of genome integrity. dCTP deaminases and the bifunctional dCTP deaminase-dUTPases are cooperatively regulated by dTTP. However, the manifestation of allosteric behavior within the same trimeric protein architecture of dUTPases, the third member of the superfamily, has been a question of debate for decades. Therefore, we designed hybrid dUTPase trimers to access conformational states potentially mimicking the ones observed in the cooperative relatives. We studied how the interruption of different steps of the enzyme cycle affects the active site cross talk. We found that subunits work independently in dUTPase. The experimental results combined with a comparative structural analysis of dUTPase superfamily enzymes revealed that subtile structural differences within the allosteric loop and the central channel in these enzymes give rise to their dramatically different cooperative behavior. We demonstrate that the lack of allosteric regulation in dUTPase is related to the functional adaptation to more efficient dUTP hydrolysis which is advantageous in uracil-DNA prevention.
Asymmetric hybrid enzymes exhibit non-cooperative kinetics in the different reaction steps.
(a) Schematic representation of the created hybrids (covalent heterotrimers). Blue, red and yellow spheres represent dUTPase protomers containing the D102N, A98F and T148STOP mutations, respectively. Note, that all protomers contain the F158W mutation as well, except for the T148STOP mutant. Grey areas indicate enzymatic inactivity. (b) Steady-state kinetics of human dUTPase constructs: WWW (solid square), WWN (solid triangles), WNN (open triangles), WWF (solid stars), WWS (solid circle). Smooth lines through the data are hyperbolic fits yielding Vmax= 7.9 ± 0.5 s−1 for WWW, Vmax = 4.4 ± 0.2 s−1 for WWF, Vmax = 3.8 ± 0.2 s−1 for WWN, Vmax = 1.8 ± 0.1 s−1 for WNN, Vmax = 2.9 ± 0.3 s−1 for WWS. KM values are listed in Table 1. (c) Comparison of the catalytic constants (striped bar) and apparent catalytic constants (grey bar) for determined by single turnover (transient kinetics) and steady-state experiments, respectively. See also Table 1 for the data. (d) Fluorescence intensity titrations upon dUTP binding to the various dUTPase constructs measured by stopped-flow (the symbol code is identical to that in panel (b). Smooth lines through data are hyperbolic fits yielding Kd values summarized in Table 1.