Binding of six nucleotide cofactors to the hexameric helicase RepA protein of plasmid RSF1010. 2. Base specificity, nucleotide structure, magnesium, and salt effect on the cooperative binding of the cofactors

Maria J. Jezewska, Aaron L. Lucius, Wlodzimierz Bujalowski

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16 Citations (Scopus)

Abstract

Interactions of the RepA hexameric helicase with nucleotide cofactors have been examined using nucleotide analogues, TNP-ADP and TNP-ATP, and unmodified nucleotides. Thermodynamic parameters for the interactions of modified and unmodified nucleotides have been obtained using quantitative fluorescence titration and competition titration methods. The intrinsic binding constant of ATP is by a factor of ∼10 and ∼1000 higher than the value observed for ADP and PO4 -. The data suggest that helicase acquires free-energy transducing capabilities when associated with the ssDNA, thus, forming a "holoenzyme". ATP binding is characterized by significantly stronger negative cooperativity than ADP. The cooperative interactions are predominantly induced through the specific interactions of the γ phosphate and the ribose with the protein. The salt effect on cofactor binding indicates a very different nature of the intrinsic and cooperative interactions. Surprisingly, binding of Mg2+, to both the cofactor and helicase, predominantly controls the ADP-RepA interactions. Mg2+ cations seem to play a role in affecting the distribution of high and low ssDNA-affinity states, through the strong effect on the diphosphate versus triphosphate binding. The data indicate that Mg2+ has a dual function in nucleotide-helicase interactions. At low [Mg2+], NTP binds stronger than NDP and the enzyme is predominantly in the high ssDNA-affinity state. At higher [Mg2+], NTP binds weaker than NDP and the helicase subunits can exist in alternating low- and high-affinity states that facilitate the efficient dsDNA unwinding. The RepA helicase shows a preference toward purine nucleotides. The cooperative interactions are independent of the type of the base.

Original languageEnglish (US)
Pages (from-to)3877-3890
Number of pages14
JournalBiochemistry
Volume44
Issue number10
DOIs
StatePublished - Mar 15 2005

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Magnesium
Plasmids
Nucleotides
Salts
Adenosine Diphosphate
Proteins
Titration
Adenosine Triphosphate
Purine Nucleotides
Holoenzymes
Ribose
Diphosphates
Thermodynamics
Free energy
Cations
Fluorescence
Phosphates
Enzymes

ASJC Scopus subject areas

  • Biochemistry

Cite this

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title = "Binding of six nucleotide cofactors to the hexameric helicase RepA protein of plasmid RSF1010. 2. Base specificity, nucleotide structure, magnesium, and salt effect on the cooperative binding of the cofactors",
abstract = "Interactions of the RepA hexameric helicase with nucleotide cofactors have been examined using nucleotide analogues, TNP-ADP and TNP-ATP, and unmodified nucleotides. Thermodynamic parameters for the interactions of modified and unmodified nucleotides have been obtained using quantitative fluorescence titration and competition titration methods. The intrinsic binding constant of ATP is by a factor of ∼10 and ∼1000 higher than the value observed for ADP and PO4 -. The data suggest that helicase acquires free-energy transducing capabilities when associated with the ssDNA, thus, forming a {"}holoenzyme{"}. ATP binding is characterized by significantly stronger negative cooperativity than ADP. The cooperative interactions are predominantly induced through the specific interactions of the γ phosphate and the ribose with the protein. The salt effect on cofactor binding indicates a very different nature of the intrinsic and cooperative interactions. Surprisingly, binding of Mg2+, to both the cofactor and helicase, predominantly controls the ADP-RepA interactions. Mg2+ cations seem to play a role in affecting the distribution of high and low ssDNA-affinity states, through the strong effect on the diphosphate versus triphosphate binding. The data indicate that Mg2+ has a dual function in nucleotide-helicase interactions. At low [Mg2+], NTP binds stronger than NDP and the enzyme is predominantly in the high ssDNA-affinity state. At higher [Mg2+], NTP binds weaker than NDP and the helicase subunits can exist in alternating low- and high-affinity states that facilitate the efficient dsDNA unwinding. The RepA helicase shows a preference toward purine nucleotides. The cooperative interactions are independent of the type of the base.",
author = "Jezewska, {Maria J.} and Lucius, {Aaron L.} and Wlodzimierz Bujalowski",
year = "2005",
month = "3",
day = "15",
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language = "English (US)",
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pages = "3877--3890",
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T1 - Binding of six nucleotide cofactors to the hexameric helicase RepA protein of plasmid RSF1010. 2. Base specificity, nucleotide structure, magnesium, and salt effect on the cooperative binding of the cofactors

AU - Jezewska, Maria J.

AU - Lucius, Aaron L.

AU - Bujalowski, Wlodzimierz

PY - 2005/3/15

Y1 - 2005/3/15

N2 - Interactions of the RepA hexameric helicase with nucleotide cofactors have been examined using nucleotide analogues, TNP-ADP and TNP-ATP, and unmodified nucleotides. Thermodynamic parameters for the interactions of modified and unmodified nucleotides have been obtained using quantitative fluorescence titration and competition titration methods. The intrinsic binding constant of ATP is by a factor of ∼10 and ∼1000 higher than the value observed for ADP and PO4 -. The data suggest that helicase acquires free-energy transducing capabilities when associated with the ssDNA, thus, forming a "holoenzyme". ATP binding is characterized by significantly stronger negative cooperativity than ADP. The cooperative interactions are predominantly induced through the specific interactions of the γ phosphate and the ribose with the protein. The salt effect on cofactor binding indicates a very different nature of the intrinsic and cooperative interactions. Surprisingly, binding of Mg2+, to both the cofactor and helicase, predominantly controls the ADP-RepA interactions. Mg2+ cations seem to play a role in affecting the distribution of high and low ssDNA-affinity states, through the strong effect on the diphosphate versus triphosphate binding. The data indicate that Mg2+ has a dual function in nucleotide-helicase interactions. At low [Mg2+], NTP binds stronger than NDP and the enzyme is predominantly in the high ssDNA-affinity state. At higher [Mg2+], NTP binds weaker than NDP and the helicase subunits can exist in alternating low- and high-affinity states that facilitate the efficient dsDNA unwinding. The RepA helicase shows a preference toward purine nucleotides. The cooperative interactions are independent of the type of the base.

AB - Interactions of the RepA hexameric helicase with nucleotide cofactors have been examined using nucleotide analogues, TNP-ADP and TNP-ATP, and unmodified nucleotides. Thermodynamic parameters for the interactions of modified and unmodified nucleotides have been obtained using quantitative fluorescence titration and competition titration methods. The intrinsic binding constant of ATP is by a factor of ∼10 and ∼1000 higher than the value observed for ADP and PO4 -. The data suggest that helicase acquires free-energy transducing capabilities when associated with the ssDNA, thus, forming a "holoenzyme". ATP binding is characterized by significantly stronger negative cooperativity than ADP. The cooperative interactions are predominantly induced through the specific interactions of the γ phosphate and the ribose with the protein. The salt effect on cofactor binding indicates a very different nature of the intrinsic and cooperative interactions. Surprisingly, binding of Mg2+, to both the cofactor and helicase, predominantly controls the ADP-RepA interactions. Mg2+ cations seem to play a role in affecting the distribution of high and low ssDNA-affinity states, through the strong effect on the diphosphate versus triphosphate binding. The data indicate that Mg2+ has a dual function in nucleotide-helicase interactions. At low [Mg2+], NTP binds stronger than NDP and the enzyme is predominantly in the high ssDNA-affinity state. At higher [Mg2+], NTP binds weaker than NDP and the helicase subunits can exist in alternating low- and high-affinity states that facilitate the efficient dsDNA unwinding. The RepA helicase shows a preference toward purine nucleotides. The cooperative interactions are independent of the type of the base.

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