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Beta-L-thymidine 5'-triphosphate analogs as DNA polymerase substrates
N A Van Draanen1, S C Tucker, F L Boyd
1Division of Experimental Therapy, Wellcome Research Laboratories, Research Triangle Park, North Carolina 27709.
The Journal of Biological Chemistry
|December 15, 1992
Summary
L-nucleoside triphosphate analogs like L-ddTTP are substrates for key DNA polymerases, but with lower efficiency than their D-enantiomers. These findings reveal insights into DNA polymerase substrate recognition and drug development.
Area of Science:
- Molecular Biology
- Enzymology
- Virology
Background:
- Nucleoside triphosphate analogs are crucial in antiviral therapies, particularly against human immunodeficiency virus (HIV).
- Understanding the substrate specificity of viral reverse transcriptases and host DNA polymerases is vital for designing effective inhibitors.
Purpose of the Study:
- To investigate the substrate and inhibitory properties of beta-L-3'-Deoxythymidine 5'-triphosphate (L-ddTTP) and beta-L-3'-deoxy-2',3'-didehydrothymidine 5'-triphosphate (L-d4TTP).
- To compare the enzymatic activity of L-nucleoside triphosphate analogs with their D-enantiomers across different DNA polymerases.
Main Methods:
- Enzymatic assays were performed using human immunodeficiency virus reverse transcriptase, Escherichia coli DNA polymerase I (Klenow fragment), and Sequenase (modified T7 DNA polymerase).
- Kinetic parameters, including Km, Kd, and kcat values, were determined for the incorporation of L- and D-nucleoside triphosphate analogs.
- Inhibition assays were conducted using beta-D- and beta-L-enantiomers of 5-methyluridine 5'-triphosphate (rTTP).
Main Results:
- L-ddTTP and L-d4TTP were substrates for all tested enzymes, but exhibited significantly higher Km values (12-70-fold) compared to their D-enantiomers.
- Reverse transcriptase and Sequenase showed similar kcat values for L- and D-enantiomers, suggesting enzyme-chain-terminated complex dissociation as the rate-limiting step.
- Klenow polymerase displayed drastically reduced kcat values for L-enantiomers (0.1% of dTTP) and D-enantiomers (15% of dTTP), indicating a shift in the rate-limiting step to catalysis.
Conclusions:
- These DNA polymerases do not stereospecifically recognize D-nucleoside 5'-triphosphate analogs as substrates.
- The differential kinetic behavior highlights distinct mechanisms of substrate processing among different DNA polymerases.
- Findings provide valuable data for the rational design of nucleoside analog-based antiviral and therapeutic agents.