Structural Basis of Drug Resistance Due to Lys103Asn Mutation Suggested by Crystal Structures of Unliganded and Inhibitor-Bound Lys103Asn HIV-1 RT. Yu Hsiou, Jianping Ding, Kalyan Das, Art Clark, Jr., Jörg-Peter Kleim¹, Manfred Rösner¹, Paul A.J. Janssen², Stephen H. Hughes³, and Edward Arnold^*, Center for Advanced Biotechnology and Medicine (CABM) and Rutgers University Chemistry Department, 679 Hoes Lane, Piscataway, NJ 08854-5638, USA; ¹Hoechst AG, General Pharma Research, G 838, 65926 Frankfurt, Germany; ²Center for Molecular Design, Janssen Research Foundation, Antwerpsesteenweg 37, B-2350, Vosselaer, Belgium; ³ABL-Basic Research Program, NCI-Frederick Cancer Research and Development Center, Building 539, P.O. Box B, Frederick, MD 21702-1201, USA.

Substitution of asparagine for lysine at position 103 of HIV-1 reverse transcriptase (RT) corresponds to a resistance mutation commonly seen during monotherapy with many nonnucleoside RT inhibitors (NNRTIs). The Lys103Asn RT variant confers relatively high-level resistance (~50-100 fold) against nevirapine, a-APA, TIBO, and BHAP (Richman et al., Antimicrob. Agents Chemother., 1993, 37, 1207-1213; Balzarini et al., J. Virol., 1993, 43, 109-114; Demeter et al., Third Workshop on Viral Resistance, 1993; Staszewski et al., Antivirol Therapy, 1996, 1, 42-50). Using synchrotron radiation at CHESS, we have determined the structures of the Lys103Asn HIV-1 mutant RT complexed with HBY 097 at 2.8 Å resolution, and with a-APA at 3.0 Å resolution. The Lys103Asn mutant RT/inhibitor complexes crystallized in space group C2, with cell parameters comparable to those of other RT/inhibitor complexes. Both HBY 097 and a-APA bind in the hydrophobic pocket near the polymerase active site in a similar manner as they do with wild type RT. Observation of a similar binding mode suggests that the inhibitors interact with both wild type and Lys103Asn mutant HIV-1 RT in an analogous manner. Subtle changes in the mutant RT/inhibitor complexes are observed mainly in the NNIBP region. We have also determined the crystal structure of an unliganded Lys103Asn mutant HIV-1 RT at 2.7 Å resolution. Significant differences occur in the loop region containing the Lys103Asn mutation in the p66 subunit that may account for the relatively uniform drug resistance against many NNRTIs. Comparison between the structures of unliganded mutant RT and the mutant RT/inhibitor complexes will help us to further understand the mechanisms of inhibition and resistance. Detailed structural information will be presented.