HIGH-RESOLUTION STRUCTURE OF THE CATALYTIC DOMAIN OF AVIAN-SARCOMA VIRUS INTEGRASE

Retroviral integrase (IN) functions to insert retroviral DNA into the host cell chromosome in a highly coordinated manner. IN catalyzes two biochemically separable reactions: processing of the viral DNA ends an d joining of these ends to the host DNA. Previous studies suggested th at these two reactions are chemically similar and are carried out by a single active site that is characterized by a highly conserved conste llation of carboxylate residues, the D,D(35)E motif. We report here th e crystal structure of the isolated catalytic domain of avian sarcoma virus (ASV) IN, solved using multiwavelength anomalous diffraction dat a for a selenomethionine derivative and refined at 1.7 Angstrom resolu tion. The protein is a crystallographic dimer with each monomer featur ing a five-stranded mixed beta-sheet region surrounded by five alpha-h elices. Based on the general fold and the arrangement of catalytic car boxylate residues, it is apparent that ASV IN is a member of a superfa mily of proteins that also includes two types of nucleases, RuvC and R Nase H. The general fold and the dimer interface are similar to those of the analogous domain of HIV-1 IN, whose crystal structure has been determined at 2.5 Angstrom resolution. However, the ASV IN structure i s more complete in that all three critical carboxylic acids, Asp64, As p121 and Glu157, are ordered. The ordered active site and the consider ably higher resolution of the present structure are all important to a n understanding of the mechanism of retroviral DNA integration, as wel l as for designing antiviral agents that may be effective against HIV.