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Selective excision of AZTMP by drug-resistant human immunodeficiency virus reverse transcriptase
P L Boyer1, S G Sarafianos, E Arnold
1ABL Basic Research Program, National Cancer Institute Frederick Cancer Research and Development Center, Frederick, Maryland 21702-1201, USA.
Journal of Virology
|April 20, 2001
Summary
HIV-1 reverse transcriptase (RT) resistance to zidovudine (AZT) involves enhanced ATP binding by mutations, facilitating analog excision. Specificity for AZT stems from active site interactions with its azido group, not resistance mutations.
Area of Science:
- Molecular Biology
- Virology
- Biochemistry
Background:
- HIV-1 reverse transcriptase (RT) exhibits resistance to nucleoside analogs through two main mechanisms: impaired incorporation or enhanced excision.
- While impaired incorporation is well-established, the role of enhanced excision in zidovudine (AZT) resistance is a recent proposal requiring further mechanistic explanation.
Purpose of the Study:
- To elucidate the mechanisms by which AZT resistance mutations enhance analog excision.
- To understand the basis for the specificity of the excision reaction for AZT.
Main Methods:
- Integration of structural and biochemical data to develop a mechanistic model.
- Analysis of the role of ATP binding and active site interactions in AZT excision.
Main Results:
- AZT resistance mutations enhance the binding affinity of HIV-1 RT for ATP, the likely physiological pyrophosphate donor.
- This increased ATP affinity promotes efficient excision of incorporated AZT at physiological ATP concentrations.
- Excision specificity for AZT-terminated primers is determined by steric interactions between the azido group of AZT and the RT active site, not by resistance mutations.
Conclusions:
- HIV-1 RT resistance to AZT is mediated by mutations that enhance ATP binding, thereby promoting analog excision.
- The active site's structural configuration and its interaction with the azido group of AZT confer specificity to the excision process.