Resistance of HIV-1 reverse transcriptase against [2',5'-bis-O-(tert-butyldimethylsilyl)-3'-spiro-5“-(4”-amino-1“,2”- oxathiole-2“,2”-dioxide)] (TSAO) derivatives is determined by the mutation Glu138–>Lys on the p51 subunit.

Potential Multifunctional Inhibitors of HIV-1 Reverse Transcriptase. Novel [AZT]-[TSAO-T] and [d4T]-[TSAO-T] Heterodimers Modified in the Linker and in the Dideoxynucleoside Region

“…Among NNRTIs, the TSAO nucleosides , occupy a unique position in that they interfere at the interface between the p51 and p66 subunits of HIV-1 RT 13a. Well-defined amino acids at both the p51 and p66 RT subunits are needed for an optimum interaction of TSAO with the HIV-1 RT. − Our experimental data strongly suggest a specific interaction of the 3‘-spiro moiety of TSAO molecules with the glutamic acid residue at position 138 (Glu-138) of the p51 subunit of HIV-1 RT. 13b, …”

Peptides Mimicking the β7/β8 Loop of HIV-1 Reverse Transcriptase p51 as “Hotspot-Targeted” Dimerization Inhibitors

“…21,26 Nonconservative substitutions of those amino acids [29][30][31][32] must have a large impact on the RT heterodimer interface because they often render catalytically inactive enzymes. [27][28][29] Alanine-scanning mutagenesis of Ser134, Ile135, Asn136, Asn137, Thr139 and Pro149 residues 31 corroborated the pivotal role of Asn136 in HIV-1 RT heterodimer stability and function. [30][31][32] Figure 2.…”

“… Therefore, TSAO-T was the first example of a small nonpeptide molecule that inhibits the dimerization process of the enzyme upon transient binding to the β7-β8 of the p51 subunit. − On the basis of results from computational studies it was proposed that TSAO molecules bind at the p66/p51 dimer interface, making extensive use of the β7-β8 loop of the p51 subunit . In fact, a key interaction for TSAO molecules binding to HIV-1 RT involves Glu138 in the β7-β8 loop, and TSAO derivatives consistently select for a E138 K resistance mutation in HIV-1 RT; hence, this loop was identified as a “hotspot” for enzyme dimerization . In addition, the crystal structure of the HIV-1 RT/TSAO-T complex showed a hyperexpansion of the NNRTI-binding pocket (NNIBP) and a significant rearrangement of RT subdomains .…”

“…Moreover, the backbone of p51 Asn136 also interacts through hydrogen bonds with Thr181 and Val381 of the p66 subunit. On the other hand, Glu138 (key residue for TSAO molecules) interacts with the side chains of Tyr181 and Lys103 of the p66 subunit, thus contributing to the heterodimer’s stability. , Nonconservative substitutions of those amino acids − must have a large impact on the RT heterodimer interface because they often render catalytically inactive enzymes. − Alanine-scanning mutagenesis of Ser134, Ile135, Asn136, Asn137, Thr139, and Pro149 residues corroborated the pivotal role of Asn136 in HIV-1 RT heterodimer stability and function. − …”

HIV-1 Drug Resistance

“…This mutation shows synergy with Y181C for resistance to NNRTIs (25). A mutation at codon 138 confers resistance only to some NNRTIs (20,26) owing to changes that affect the p51 rather than the p66 subunit.…”