TY - JOUR
T1 - Escherichia coli DnaB helicase-DnaC protein complex
T2 - Allosteric effects of the nucleotides on the nucleic acid binding and the kinetic mechanism of NTP hydrolysis. 3
AU - Roychowdhury, Anasuya
AU - Szymanski, Michal R.
AU - Jezewska, Maria J.
AU - Bujalowski, Wlodzimierz
PY - 2009/7/28
Y1 - 2009/7/28
N2 - Allosteric interactions between the DNA- and NTP-binding sites of the Escherichia coli DnaB helicase engaged in the DnaB-DnaC complex and the mechanism of NTP hydrolysis by the complex have been examined using the fluorescence titration, analytical ultracentrifugation, and rapid quench-flow technique. Surprisingly, the ssDNA affinity of the DnaB-DnaC complex is independent of the structure of the phosphate group of the cofactor bound to the helicase. Thus, the DnaC protein eliminates the antagonistic allosteric effect of NTP and NDP on the ssDNA affinity of the enzyme. The protein changes the engagement of the DNA-binding subsites of the helicase in interactions with the nucleic acid, depending on the structure of the phosphate group of the present nucleotide cofactor and profoundly affects the structure of the bound DNA. Moreover, the ssDNA affinity of the helicase in the DnaB-DnaC complex is under the control of the nucleotide-binding site of the DnaC protein. The protein does not affect the NTP hydrolysis mechanism of the helicase. Nevertheless, the rate of the chemical step is diminished in the DnaB-DnaC complex. In the tertiary DnaB-DnaC-ssDNA complex, the ssDNA changes the internal dynamics between intermediates of the pyrimidine cofactor, in a manner independent of the base composition of the DNA, while the hydrolysis step of the purine cofactor is specifically stimulated by the homoadenosine ssDNA. The significance of these results for functional activities of the DnaB-DnaC complex is discussed.
AB - Allosteric interactions between the DNA- and NTP-binding sites of the Escherichia coli DnaB helicase engaged in the DnaB-DnaC complex and the mechanism of NTP hydrolysis by the complex have been examined using the fluorescence titration, analytical ultracentrifugation, and rapid quench-flow technique. Surprisingly, the ssDNA affinity of the DnaB-DnaC complex is independent of the structure of the phosphate group of the cofactor bound to the helicase. Thus, the DnaC protein eliminates the antagonistic allosteric effect of NTP and NDP on the ssDNA affinity of the enzyme. The protein changes the engagement of the DNA-binding subsites of the helicase in interactions with the nucleic acid, depending on the structure of the phosphate group of the present nucleotide cofactor and profoundly affects the structure of the bound DNA. Moreover, the ssDNA affinity of the helicase in the DnaB-DnaC complex is under the control of the nucleotide-binding site of the DnaC protein. The protein does not affect the NTP hydrolysis mechanism of the helicase. Nevertheless, the rate of the chemical step is diminished in the DnaB-DnaC complex. In the tertiary DnaB-DnaC-ssDNA complex, the ssDNA changes the internal dynamics between intermediates of the pyrimidine cofactor, in a manner independent of the base composition of the DNA, while the hydrolysis step of the purine cofactor is specifically stimulated by the homoadenosine ssDNA. The significance of these results for functional activities of the DnaB-DnaC complex is discussed.
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U2 - 10.1021/bi9000535
DO - 10.1021/bi9000535
M3 - Article
C2 - 19432487
AN - SCOPUS:67651222269
SN - 0006-2960
VL - 48
SP - 6747
EP - 6763
JO - Biochemistry
JF - Biochemistry
IS - 29
ER -