Abstract
Human immunodeficiency virus (HIV-1) develops resistance to
3′-azido-2′,3′-deoxythymidine (AZT, zidovudine) by
acquiring mutations in reverse transcriptase that enhance the ATP-mediated
excision of AZT monophosphate from the 3′ end of the primer. The excision
reaction occurs at the dNTP-binding site, uses ATP as a pyrophosphate donor,
unblocks the primer terminus and allows reverse transcriptase to continue viral
DNA synthesis. The excision product is AZT adenosine dinucleoside tetraphosphate
(AZTppppA). We determined five crystal structures: wild-type reverse
transcriptase–double-stranded DNA (RT–dsDNA)–AZTppppA;
AZT-resistant (AZTr; M41L D67N K70R T215Y K219Q)
RT–dsDNA–AZTppppA; AZTr RT–dsDNA terminated with AZT at
dNTP- and primer-binding sites; and AZTr apo reverse transcriptase. The AMP part
of AZTppppA bound differently to wild-type and AZTr reverse transcriptases,
whereas the AZT triphosphate part bound the two enzymes similarly. Thus, the
resistance mutations create a high-affinity ATP-binding site. The structure of
the site provides an opportunity to design inhibitors of AZT-monophosphate
excision.