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  • 1
    ISSN: 1432-1327
    Keywords: Key words Human immunodeficiency virus type 1 reverse transcriptase ribonuclease H domain ; Calorimetry ; Metal binding ; Mechanism ; Stoichiometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  Crystallographic studies of the Mn2+-doped RNase H domain of human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT) [1] have revealed two bound Mn2+ separated by approximately 4 Å and surrounded by a cluster of four conserved carboxylates. Escherichia coli RNase H is structurally similar to the RNase H domain of HIV-1 RT, but requires one divalent metal cation for its activity [2, 3], implying either that the HIV-1 RT RNase H domain contrasts in its ability to bind two divalent metal ions, or that the crystallographic data reflect specific use of Mn2+ and/or the doping technique employed. Metal binding stoichiometry has been determined for Mn2+ and the biologically more relevant Mg2+ cation by solution calorimetric studies of native and recombinant p66/p51 HIV-1 RT. Three Mn2+ ions bind to HIV-1 RT apo-enzyme: one at the DNA polymerase and two at the RNase H catalytic center, the latter being consistent with crystallographic results. However, only one Mg2+ ion is bound in the RNase H catalytic center. Several mechanistic implications arise from these results, including the possibility of mutually exclusive Mg2+ binding sites that might be occupied according to the specific reaction being catalyzed by the multifunctional RNase H domain. The occurrence of distinct binding stoichiometries for Mg2+ and Mn2+ to multifunctional enzymes has previously been reported [4].
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1327
    Keywords: Key words Magnesium binding ; RNA ; Polyelectrolyte ; Calorimetry ; 25Mg NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  Binding of divalent magnesium to RNA homopolymers was evaluated by titration calorimetry and analyzed in terms of the McGhee and von Hippel model of a one-dimensional infinite lattice. Examination of Mg2+ binding data for ds poly(A)×poly(U), ss poly(A), and ss poly(U) revealed that the sign of the enthalpy term relates to the mode of metal binding (inner or outer sphere), which in turn is directly related to the structural ordering of the polynucleotide in solution. This approach provides details of the thermodynamics of metal binding, stoichiometry, and coordination chemistry that underlie the structural and catalytic chemistry of RNA and offers a potential new probe of the solution structure of nucleic acids.
    Type of Medium: Electronic Resource
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