Structural determinants of metal-induced conformational changes in HIV-1 integrase.

Human immunodeficiency virus type 1 (HIV-1) integrase (IN) undergoes a reversible metal-induced conformational change that activates the enzyme (Asante-Appiah, E., and Skalka, A. M. (1997) J. Biol. Chem. 272, 16196-16205). In this report, key structural features that mediate this conformational change have been identified by site-directed mutagenesis, limited proteolysis, and mass spectrometry studies. The results reveal two separable metal-induced effects. One depends on residues in the N-terminal domain (amino acids 1-50) and a C-terminal tail (amino acids 274-288) and is detected by increased resistance of the full-length protein to proteolytic digestion. This effect appears to depend on metal binding at an undefined location distinct from the known sites in the N-terminal and catalytic core domains. The second conformational change depends on metal binding at the active site in the catalytic core domain. Substitution of acidic residues Asp64 or Glu152 in the catalytic core D,D(35)E motif or truncation of the Src homology 3 (SH3)-like domain in the C-terminal region of the enzyme abolishes this metal-induced change. Comparison of tryptic digests of an HIV-1 IN derivative competent for metal-induced conformational change and a conformation-defective D64N derivative identified specific regions in HIV-1 IN that are affected by this second change. A region in the N terminus that spans Lys14, an extended loop and the adjacent region in the core domain (including lysines 136, 156, and 160 and Arg173), and residues at the C terminus beyond the SH3-like domain all become less accessible to proteolysis in the conformation-competent protein. In contrast, a region that encompasses Lys258 in the putative DNA binding groove of the SH3-like domain becomes more sensitive to proteolysis in the presence of Mn2+. The results are consistent with a model in which the binding of the metal ion by residues of the D,D(35)E motif elicits specific changes in all three domains of HIV-1 IN, inducing the restructuring of the enzyme for catalytic competence.