The role of Thr139 in the human immunodeficiency virus type 1 reverse transcriptase sensitivity to (+)-calanolide A

Mol Pharmacol. 2005 Sep;68(3):652-9. doi: 10.1124/mol.105.012351. Epub 2005 Jun 16.


The coumarins represent a unique class of non-nucleoside reverse transcriptase inhibitors (NNRTIs) that were isolated from tropical plants. (+)-Calanolide A, the most potent compound of this class, selects for the T139I resistance mutation in HIV-1 reverse transcriptase (RT). Seven RTs mutated at amino acid position 139 (Ala, Lys, Tyr, Asp, Ile, Ser, and Gln) were constructed by site-directed mutagenesis. The mutant T139Q enzyme retained full catalytic activity compared with wild-type RT, whereas the mutant T139I, T139S, and T139A RTs retained only 85 to 50% of the activity. Mutant T139K, T139D, and T139Y RTs had seriously impaired catalytic activities. The mutations in the T139I and T139D RTs were shown to destabilize the RT heterodimer. (+)-Calanolide A lost inhibitory activity (up to 20-fold) against the mutant T139Y, T139Q, T139K, and T139I enzymes. All of the mutant enzymes retained marked susceptibility toward the other NNRTIs, including nevirapine, delavirdine, efavirenz, thiocarboxanilide UC-781, quinoxaline GW867420X, TSAO [[2',5'-bis-O-(tert-butyldimethylsilyl)-beta-D-ribofuranosyl]-3'-spiro-5''-(4''-amino-1'',2''-oxathiole-2'',2''-dioxide)] derivatives, and the nucleoside inhibitor, ddGTP. The fact that the T139I RT 1) proved to be resistant to (+)-calanolide A, 2) represents a catalytically efficient enzyme, and 3) requires only a single transition point mutation (ACA-->ATA) in codon 139 seems to explain why mutant T139I RT virus strains, but not virus strains containing other amino acid changes at this position, predominantly emerge in cell cultures under (+)-calanolide A pressure.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Coumarins / pharmacology*
  • HIV Reverse Transcriptase / antagonists & inhibitors*
  • HIV Reverse Transcriptase / chemistry
  • HIV Reverse Transcriptase / genetics
  • Kinetics
  • Models, Molecular
  • Mutagenesis, Site-Directed
  • Pyranocoumarins
  • Reverse Transcriptase Inhibitors / pharmacology*
  • Threonine / chemistry
  • Threonine / physiology*


  • Coumarins
  • Pyranocoumarins
  • Reverse Transcriptase Inhibitors
  • Threonine
  • HIV Reverse Transcriptase
  • calanolide A