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Metal-ion stoichiometry of the HIV-1 RT ribonuclease H domain: evidence for two mutually exclusive sites leads to new mechanistic insights on metal-mediated hydrolysis in nucleic acid biochemistry.
Cowan JA; Ohyama T; Howard K; Rausch JW; Cowan SM; Le Grice SF; Evans
August 30, 2000
J Biol Inorg Chem. 2000 Feb;5(1):67-74. Unique Identifier : AIDSLINE

Crystallographic studies of the Mn(2+)-doped RNase H domain of human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT) have revealed two bound Mn2+ separated by approximately 4A 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, 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.

JOURNAL ARTICLE Calorimetry Crystallography, X-Ray Hydrolysis HIV-1 Reverse Transcriptase/CHEMISTRY/GENETICS/*METABOLISM Manganese/*METABOLISM Models, Molecular Nucleic Acids/*METABOLISM Protein Binding Protein Conformation Recombinant Proteins/CHEMISTRY/GENETICS/METABOLISM Ribonuclease H, Calf Thymus/*METABOLISM Support, Non-U.S. Gov't Support, U.S. Gov't, Non-P.H.S. Support, U.S. Gov't, P.H.S. Thermodynamics

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