W0068

Structure of the Catalytic Domain of Avian Sarcoma Virus Integrase with Bound HIV-1 IN Inhibitor. Jerry Alexandratos, Jacek Lubkowski, Fan Yang, and Alexander Wlodawer, Macromolecular Structure Laboratory, ABL-BRP, NCI-FCRDC, Frederick, MD 21702; He Zhao, Terrence R. Burke, Jr., Laboratory of Medicinal Chemistry, Nouri Neamati, Yves Pommier, Laboratory of Molecular Pharmacology, NCI, NIH, Bethesda, MD 20892; George Merkel and Anna Marie Skalka, ICR, Fox Chase Cancer Center, Philadelphia PA 19111

The x-ray structures of an inhibitor complex of the catalytic core domain of avian sarcoma virus integrase (ASV IN) were solved at 1.9-2.0 resolution at two pH values, with and without Mn²⁺ cations. This inhibitor (Y-3), originally identified in a screen for inhibitors of the catalytic activity of human immunodeficiency virus type 1 integrase (HIV-1 IN), was found in the present study to be active against ASV IN as well as HIV-1 IN. The structures revealed details of the inhibitor binding site, located in close proximity to the enzyme active site. The inhibitor molecule interacts with the flexible loop near the active site, altering the loop conformation and affecting the conformations of the active site residues. In the crystal structure, an inhibitor molecule is stacked against its symmetry-related mate. Preincubation of IN with metal cations does not affect the ability of the compound to inhibit enzymatic activity; furthermore inhibitor binding does not interfere with the ability of the enzyme to bind divalent cations. Three other compounds chemically related to the inhibitor were also investigated, but no binding of these compounds was observed in the crystals of ASV IN. Our results identify structural elements of the inhibitor molecule that most likely determine its binding properties. Research sponsored in part by the National Cancer Institute, DHHS, under contract with ABL.