scholarly journals Structures of Reverse Transcriptase Pre- and Post-Excision Complexes Shed New Light on HIV-1 AZT Resistance

Viruses ◽  
2011 ◽  
Vol 3 (1) ◽  
pp. 20-25 ◽  
Author(s):  
Walter A. Scott
Keyword(s):  
Reverse Transcriptase ◽  
Azt Resistance ◽  
Hiv 1

scholarly journals Selective Excision of AZTMP by Drug-Resistant Human Immunodeficiency Virus Reverse Transcriptase

2001 ◽  
Vol 75 (10) ◽  
pp. 4832-4842 ◽  
Author(s):  
Paul L. Boyer ◽  
Stefan G. Sarafianos ◽  
Edward Arnold ◽  
Stephen H. Hughes
Keyword(s):  
Human Immunodeficiency Virus ◽  
Reverse Transcriptase ◽  
Nucleoside Analogs ◽  
Azido Group ◽  
Resistance Mutations ◽  
Immunodeficiency Virus ◽  
Azt Resistance ◽  
Hiv 1

ABSTRACT Two distinct mechanisms can be envisioned for resistance of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) to nucleoside analogs: one in which the mutations interfere with the ability of HIV-1 RT to incorporate the analog, and the other in which the mutations enhance the excision of the analog after it has been incorporated. It has been clear for some time that there are mutations that selectively interfere with the incorporation of nucleoside analogs; however, it has only recently been proposed that zidovudine (AZT) resistance can involve the excision of the nucleoside analog after it has been incorporated into viral DNA. Although this proposal resolves some important issues, it leaves some questions unanswered. In particular, how do the AZT resistance mutations enhance excision, and what mechanism(s) causes the excision reaction to be relatively specific for AZT? We have used both structural and biochemical data to develop a model. In this model, several of the mutations associated with AZT resistance act primarily to enhance the binding of ATP, which is the most likely pyrophosphate donor in the in vivo excision reaction. The AZT resistance mutations serve to increase the affinity of RT for ATP so that, at physiological ATP concentrations, excision is reasonably efficient. So far as we can determine, the specificity of the excision reaction for an AZT-terminated primer is not due to the mutations that confer resistance, but depends instead on the structure of the region around the HIV-1 RT polymerase active site and on its interactions with the azido group of AZT. Steric constraints involving the azido group cause the end of an AZT 5′-monophosphate-terminated primer to preferentially reside at the nucleotide binding site, which favors excision.

scholarly journals The M184V Mutation Reduces the Selective Excision of Zidovudine 5′-Monophosphate (AZTMP) by the Reverse Transcriptase of Human Immunodeficiency Virus Type 1

2002 ◽  
Vol 76 (7) ◽  
pp. 3248-3256 ◽  
Author(s):  
Paul L. Boyer ◽  
Stefan G. Sarafianos ◽  
Edward Arnold ◽  
Stephen H. Hughes
Keyword(s):  
Human Immunodeficiency Virus ◽  
Reverse Transcriptase ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Published Data ◽  
Immunodeficiency Virus ◽  
Azt Resistance ◽  
Hiv 1 ◽  
M184v Mutation

ABSTRACT The M184V mutation in human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) causes resistance to lamivudine, but it also increases the sensitivity of the virus to zidovudine (3′-azido-3′-deoxythymidine; AZT). This sensitization to AZT is seen both in the presence and the absence of the mutations that confer resistance to AZT. AZT resistance is due to enhanced excision of AZT 5′-monophosphate (AZTMP) from the end of the primer by the RT of the resistant virus. Published data suggest that the excision reaction involves pyrophosphorolysis but that the likely in vivo pyrophosphate donor is not pyrophosphate but ATP. The mutations that lead to AZT resistance enhance ATP binding and, in so doing, enhance pyrophosphorolysis. The excision reaction is specific for AZT because HIV-1 RT, which can form a closed complex with a dideoxy-terminated primer and an incoming deoxynucleoside triphosphate (dNTP), does not form the closed complex with an AZTMP-terminated primer and an incoming dNTP. This means that an AZTMP-terminated primer has better access to the site where it can be excised. The M184V mutation alters the polymerase active site in a fashion that specifically interferes with ATP-mediated excision of AZTMP from the end of the primer strand. The M184V mutation does not affect the incorporation of AZT 5′-triphosphate (AZTTP), either in the presence or the absence of mutations that enhance AZTMP excision. However, in the presence of ATP, the M184V mutation does decrease the ability of HIV-1 RT to carry out AZTMP excision. Based on these results, and on the results of other excision experiments, we present a model to explain how the M184V mutation affects AZTMP excision.

scholarly journals Selection of Mutations in the Connection and RNase H Domains of Human Immunodeficiency Virus Type 1 Reverse Transcriptase That Increase Resistance to 3′-Azido-3′-Dideoxythymidine

2007 ◽  
Vol 81 (15) ◽  
pp. 7852-7859 ◽  
Author(s):  
Jessica H. Brehm ◽  
Dianna Koontz ◽  
Jeffrey D. Meteer ◽  
Vinay Pathak ◽  
Nicolas Sluis-Cremer ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Reverse Transcriptase ◽  
Rnase H ◽  
Cross Resistance ◽  
Polymerase Domain ◽  
Immunodeficiency Virus ◽  
Azt Resistance ◽  
Hiv 1

ABSTRACT Recent work indicates that mutations in the C-terminal domains of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) increase 3′-azido-3′-dideoxythymidine (AZT) resistance. Because it is not known whether AZT selects for mutations outside of the polymerase domain of RT, we carried out in vitro experiments in which HIV-1LAI or AZT-resistant HIV-1LAI (M41L/L210W/T215Y) was passaged in MT-2 cells in increasing concentrations of AZT. The first resistance mutations to appear in HIV-1LAI were two polymerase domain thymidine analog mutations (TAMs), D67N and K70R, and two novel mutations, A371V in the connection domain and Q509L in the RNase H domain, that together conferred up to 90-fold AZT resistance. Thereafter, the T215I mutation appeared but was later replaced by T215F, resulting in a large increase in AZT resistance (∼16,000-fold). Mutations in the connection and RNase H domains were not selected starting with AZT-resistant virus (M41L/L210W/T215Y). The roles of A371V and Q509L in AZT resistance were confirmed by site-directed mutagenesis: A371V and Q509L together increased AZT resistance ∼10- to 50-fold in combination with TAMs (M41L/L210W/T215Y or D67N/K70R/T215F) but had a minimal effect without TAMs (1.7-fold). A371V and Q509L also increased cross-resistance with TAMs to lamivudine and abacavir, but not stavudine or didanosine. These results provide the first evidence that mutations in the connection and RNase H domains of RT can be selected in vitro by AZT and confer greater AZT resistance and cross-resistance to nucleoside RT inhibitors in combination with TAMs in the polymerase domain.

scholarly journals Sequence Diversity of the Reverse Transcriptase of Human Immunodeficiency Virus Type 1 from Untreated Brazilian Individuals

1999 ◽  
Vol 43 (7) ◽  
pp. 1674-1680 ◽  
Author(s):  
Rodrigo Brindeiro ◽  
Bart Vanderborght ◽  
Elena Caride ◽  
Letícia Correa ◽  
Rejane M. Oravec ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Reverse Transcriptase ◽  
Human Immunodeficiency Virus Type ◽  
Direct Sequencing ◽  
Line Probe Assay ◽  
Immunodeficiency Virus ◽  
Azt Resistance ◽  
Probe Assay ◽  
Hiv 1

ABSTRACT The presence of human immunodeficiency virus type 1 (HIV-1) bearing mutations resistant to nucleosidic inhibitors of the viral reverse transcriptase (RT) derived from HIV-seropositive asymptomatic and untreated volunteer blood donors was examined. The RT amplicons of 32 specimens were analyzed by using a reverse hybridization line probe assay technique that detects resistance against zidovudine (3′-azido-3′-deoxythymidine [AZT], didanosine (2′,3′-dideoxyinosine [ddI], zalcitabine (2′,3′-dideoxycytidine [ddC]), and lamivudine {(−)-β-l-2′,3′-dideoxy-3′-thiacytidine [3TC]} at amino acid positions 41, 69, 70, 74, 184, and 215 of the HIV RT. One sample (brp004, subtype B) showed an AZT resistance secondary mutation at position K70R. Fifteen specimens revealed one or more sites of nonreactivity to both wild-type- and mutant-specific probes (dual nonreactivity). Samples were also submitted to RT direct sequencing and phylogenetic analysis. Nine of 32 specimens belonged to non-B subtypes (C, D, F, and F/B or B/F mosaics). Three of these non-B isolates, named brp004, brp063, and brp069, revealed three other relevant AZT resistance mutations—a T215F mutation and two M41L mutations, respectively—hidden by the nonreactivity to line probe assay strips on the respective codon regions. The isolate brp004 also carried a D67N AZT resistance mutation revealed by direct sequencing. No nonnucleosidic RT inhibitor-resistant mutation was found. The analysis revealed a frequency of 2.26 × 10−4 mutations per nucleotide for independent samples related to RT resistance. These findings emphasize the magnitude of naturally occurring reservoirs of drug-resistant virus among untreated HIV-1-positive individuals in Brazil.

scholarly journals Relationship between 3′-Azido-3′-Deoxythymidine Resistance and Primer Unblocking Activity in Foscarnet-Resistant Mutants of Human Immunodeficiency Virus Type 1 Reverse Transcriptase

2003 ◽  
Vol 77 (11) ◽  
pp. 6127-6137 ◽  
Author(s):  
Peter R. Meyer ◽  
Suzanne E. Matsuura ◽  
Dianna Zonarich ◽  
Rahul R. Chopra ◽  
Eric Pendarvis ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Reverse Transcriptase ◽  
Binding Site ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Resistance Mutations ◽  
Immunodeficiency Virus ◽  
Azt Resistance ◽  
Hiv 1

ABSTRACT Phosphonoformate (foscarnet) is a pyrophosphate (PPi) analogue and a potent inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT), acting through the PPi binding site on the enzyme. HIV-1 RT can unblock a chain-terminated DNA primer by phosphorolytic transfer of the terminal residue to an acceptor substrate (PPi or a nucleotide such as ATP) which also interacts with the PPi binding site. Primer-unblocking activity is increased in mutants of HIV-1 that are resistant to the chain-terminating nucleoside inhibitor 3′-azido-3′-deoxythymidine (AZT). We have compared the primer-unblocking activity for HIV-1 RT containing various foscarnet resistance mutations (K65R, W88G, W88S, E89K, S117T, Q161L, M164I, and the double mutant Q161L/H208Y) alone or in combination with AZT resistance mutations. The level of primer-unblocking activity varied over a 150-fold range for these enzymes and was inversely correlated with foscarnet resistance and directly correlated with AZT resistance. Based on published crystal structures of HIV-1 RT, many of the foscarnet resistance mutations affect residues that do not make direct contact with the catalytic residues of RT, the incoming deoxynucleoside triphosphate (dNTP), or the primer-template. These mutations may confer foscarnet resistance and reduce primer unblocking by indirectly decreasing the binding and retention of foscarnet, PPi, and ATP. Alternatively, the binding position or orientation of PPi, ATP, or the primer-template may be changed in the mutant enzyme complex so that molecular interactions required for the unblocking reaction are impaired while dNTP binding and incorporation are not.

scholarly journals In Vitro Selection of Mutations in the Human Immunodeficiency Virus Type 1 Reverse Transcriptase That Decrease Susceptibility to (−)-β-d-Dioxolane-Guanosine and Suppress Resistance to 3′-Azido-3′-Deoxythymidine

2000 ◽  
Vol 44 (7) ◽  
pp. 1783-1788 ◽  
Author(s):  
Holly Z. Bazmi ◽  
Jennifer L. Hammond ◽  
Socrates C. H. Cavalcanti ◽  
Chung K. Chu ◽  
Raymond F. Schinazi ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Dna Sequencing ◽  
Reverse Transcriptase ◽  
Genetic Background ◽  
Resistant Isolate ◽  
K65r Mutation ◽  
Immunodeficiency Virus ◽  
Azt Resistance ◽  
Hiv 1

ABSTRACT Human immunodeficiency virus type 1 (HIV-1) isolates resistant to (−)-β-d-dioxolane-guanosine (DXG), a potent and selective nucleoside analog HIV-1 reverse transcriptase (RT) inhibitor, were selected by serial passage of HIV-1LAI in increasing drug concentrations (maximum concentration, 30 μM). Two independent selection experiments were performed. Viral isolates for which the DXG median effective concentrations (EC50s) increased 7.3- and 12.2-fold were isolated after 13 and 14 passages, respectively. Cloning and DNA sequencing of the RT region from the first resistant isolate identified a K65R mutation (AAA to AGA) in 10 of 10 clones. The role of this mutation in DXG resistance was confirmed by site-specific mutagenesis of HIV-1LAI. The K65R mutation also conferred greater than threefold cross-resistance to 2′,3′-dideoxycytidine, 2′,3′-dideoxyinosine, 2′,3′-dideoxy-3′-thiacytidine, 9-(2-phosphonylmethoxyethyl)adenine, 2-amino-6-chloropurine dioxolane, dioxolanyl-5-fluorocytosine, and diaminopurine dioxolane but had only marginal effects on 3′-azido-3′-deoxthymidine (AZT) susceptibility. However, when introduced into a genetic background for AZT resistance (D67N, K70R, T215Y, T219Q), the K65R mutation reversed the AZT resistance. DNA sequencing of RT clones derived from the second resistant isolate identified the L74V mutation, previously reported to cause ddI resistance. The L74V mutation also decreased the AZT resistance when the mutation was introduced into a genetic background for AZT resistance (D67N, K70R, T215Y, T219Q) but to a lesser degree than the K65R mutation did. These findings indicate that DXG and certain 2′,3′-dideoxy compounds (e.g., ddI) can select for the same resistance mutations and thus may not be optimal for use in combination. However, the combination of AZT with DXG or its orally bioavailable prodrug (−)-β-d-2,6-diaminopurine-dioxolane should be explored because of the suppressive effects of the K65R and L74V mutations on AZT resistance.

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