Inhibition of the Ribonuclease H Activity of HIV-1 Reverse Transcriptase by GSK5750 Correlates with Slow Enzyme-Inhibitor Dissociation [Microbiology]

April 9th, 2014 by Beilhartz, G. L., Ngure, M., Johns, B. A., DeAnda, F., Gerondelis, P., Gotte, M.

Compounds that efficiently inhibit the ribonuclease (RNase) H activity of the human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) have yet to be developed. Here, we demonstrate that GSK5750, a 1-hydroxy-pyridopyrimidinone analog, binds to the enzyme with an equilibrium dissociation constant (Kd) of ∼ 400 nM. Inhibition of HIV-1 RNase H is specific, as DNA synthesis is not affected. Moreover, GSK5750 does not inhibit the activity of Escherichia Coli (E. coli) RNase H. Order-of-addition experiments show that GSK5750 binds to the free enzyme in a Mg2+-dependent fashion. However, as reported for other active site inhibitors, binding of GSK5750 to a pre-formed enzyme-substrate complex is severely compromised. The bound nucleic acid prevents access to the RNase H active site, which represents a possible biochemical hurdle in the development of potent RNase H inhibitors. Previous studies suggested that formation of a complex with the prototypic RNase H inhibitor β-thujaplicinol is slow, and, once formed, it rapidly dissociates. This unfavourable kinetic behaviour can limit the potency of RNase H active site inhibitors. Although the association kinetics of GSK5750 remains slow, our data show that this compound forms a long-lasting complex with HIV-1 RT. We conclude that slow dissociation of the inhibitor and HIV-1 RT improves RNase H active site inhibitors and may circumvent the obstacle posed by the inability of these compounds to bind to a pre-formed enzyme-substrate complex.
  • Posted in Journal of Biological Chemistry, Publications
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