Human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT) is an important target for antiviral therapy against acquired immunodeficiency syndrome. However, the efficiency of available drugs is impaired most typically by drug-resistance mutations in this enzyme. In this study, we applied a nuclear magnetic resonance (NMR) spectroscopic technique to the characterization of the binding of HIV-1 RT to various non-nucleoside reverse transcriptase inhibitors (NNRTIs) with different activities, i.e., nevirapine, delavirdine, efavirenz, dapivirine, etravirine, and rilpivirine. 1H-13C heteronuclear single-quantum coherence (HSQC) spectral data of HIV-1 RT, in which the methionine methyl groups of the p66 subunit were selectively labeled with 13C, were collected in the presence and absence of these NNRTIs. We found that the methyl 13C chemical shifts of the M230 resonance of HIV-1 RT bound to these drugs exhibited a high correlation with their anti-HIV-1 RT activities. This methionine residue is located in proximity to the NNRTI-binding pocket but not directly involved in drug interactions and serves as a conformational probe, indicating that the open conformation of HIV-1 RT was more populated with NNRTIs with higher inhibitory activities. Thus, the NMR approach offers a useful tool to screen for novel NNRTIs in developing anti-HIV drugs.

Six new 14-membered ring cyclopeptide alkaloids, cambodines A–F (1–6), and two known compounds, frangufoline (7) and lotusanine B (8), were isolated from the root bark extract ofZiziphus cambodianaPierre.

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Two-layered ONIOM calculations were performed in order to compare the binding of efavirenz (EFV) to the HIV-1 RT binding pocket of both wild type (WT) and K103N enzymes. The K103N mutation reduces the binding affinity of the inhibitor by 5.81 kcal mol À1 as obtained from the ONIOM2 (B3LYP/ 6-31G(d,p):PM3) method. These indicate that the loss of binding energy to K103N mutation can attribute to a weakened attractive interaction between the drug and residues surrounding in the binding pocket. The deformation of the K103N binding pocket requires more energy for structural rearrangement than that of the WT by approximately 4.0 kcal mol :1 . Moreover, the pairwise energies perfectly demonstrate that the K103N mutation affects on the loss of the interaction energy. In addition, the main influences are due to residues surrounding in the binding pocket; K101, K102, S105, V179, W229, P236 and E138. In particular, two residues; K101 and S105, established hydrogen bondings with the inhibitor. ONIOM calculations, resulting in the details of binding energy, interaction energy and deformation energy can be used to identify the key interaction and structural requirements of more potent HIV-1 RT inhibitor.