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Kinetic variations between reverse transcriptases of viral protein X coding and noncoding lentiviruses.

Gina M Lenzi1, Robert A Domaoal2, Dong-Hyun Kim3

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Summary
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Lentiviral reverse transcriptases (RTs) from HIV-2 and SIV have higher dNTP requirements than HIV-1 RTs, reflecting adaptations to host SAMHD1 and Vpx interactions in non-dividing cells.

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Area of Science:

  • Virology
  • Molecular Biology
  • Biochemistry

Background:

  • Host SAM domain and HD domain-containing protein 1 (SAMHD1) depletes cellular dNTPs, inhibiting HIV-1 replication in non-dividing cells.
  • HIV-2 and SIV encode viral protein X (Vpx), which counteracts SAMHD1, increasing dNTPs for viral replication.
  • This suggests lentiviruses have adapted their reverse transcriptase (RT) enzymes to varying cellular dNTP levels.

Purpose of the Study:

  • To investigate if lentiviral RTs exhibit different enzyme kinetic profiles based on dNTP concentrations.
  • To compare the kinetic parameters of RTs from HIV-1, HIV-2, and SIV strains.

Main Methods:

  • Characterization of steady-state kinetic parameters for RTs from 7 HIV-1, 4 HIV-2, and 7 SIV strains.
  • Determination of Michaelis-Menten constant (K m) and catalytic constant (k cat) values.

Main Results:

  • All HIV-1 RTs showed low K m values, aligning with low dNTP levels in macrophages.
  • HIV-2 and SIV RTs exhibited significantly higher and more variable K m values than HIV-1 RTs.
  • Catalytic efficiency (k cat) values were similar across all tested lentiviral RTs.

Conclusions:

  • Lentiviral RTs' enzymological properties, specifically K m values, are mechanistically linked to cellular dNTP availability.
  • This adaptation is influenced by the interplay between host SAMHD1 and viral Vpx in non-dividing cells.
  • The findings support a model where viral RTs are optimized for the specific dNTP environment they encounter.