Transition states of native and drug-resistant HIV-1 protease are the same

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 109; no. 17; pp. 6543 - 6548
• Main Authors: Kipp, D. Randal, Hirschi, Jennifer S, Wakata, Aya, Goldstein, Harris, Schramm, Vern L
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 24.04.2012; National Acad Sciences
• Subjects: Acquired immune deficiency syndrome; acquired immunodeficiency syndrome; Active sites; AIDS; Amides; Biochemistry; Biological Sciences; carbon; Chemical bonding; Drug resistance; Drug Resistance, Multiple; Drug Resistance, Viral; Enzymes; HIV; HIV 1; HIV Protease - chemistry; HIV Protease - metabolism; HIV-1 - drug effects; Human immunodeficiency virus; Human immunodeficiency virus 1; Hydrogen Bonding; Hydrogen bonds; isotopes; Kinetic isotope effect; Kinetics; Models, Molecular; nitrogen; Proteases; Protein Conformation; proteinases; Protons; Radiocarbon
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1202808109

HIV-1 protease is an important target for the treatment of HIV/AIDS. However, drug resistance is a persistent problem and new inhibitors are needed. An approach toward understanding enzyme chemistry, the basis of drug resistance, and the design of powerful inhibitors is to establish the structure of enzymatic transition states. Enzymatic transition structures can be established by matching experimental kinetic isotope effects (KIEs) with theoretical predictions. However, the HIV-1 protease transition state has not been previously resolved using these methods. We have measured primary 14C and 15N KIEs and secondary 3H and 18O KIEs for native and multidrug-resistant HIV-1 protease (I84V). We observed 14C KIEs (14V/K) of 1.029 ± 0.003 and 1.025 ± 0.005, 15N KIEs (15V/K) of 0.987 ± 0.004 and 0.989 ± 0.003, 18O KIEs (18V/K) of 0.999 ± 0.003 and 0.993 ± 0.003, and 3H KIEs (3V/K) KIEs of 0.968 ± 0.001 and 0.976 ± 0.001 for the native and I84V enzyme, respectively. The chemical reaction involves nucleophilic water attack at the carbonyl carbon, proton transfer to the amide nitrogen leaving group, and C-N bond cleavage. A transition structure consistent with the KIE values involves proton transfer from the active site Asp-125 (1.32 Å) with partial hydrogen bond formation to the accepting nitrogen (1.20 Å) and partial bond loss from the carbonyl carbon to the amide leaving group (1.52 Å). The KIEs measured for the native and I84V enzyme indicate nearly identical transition states, implying that a true transition-state analogue should be effective against both enzymes.