Divalent cations stimulate preferential recognition of a viral DNA end by HIV-1 integrase.

In the presence of a divalent metal cofactor (Mg2+ or Mn2+), retroviral-encoded integrase (IN) catalyzes two distinct reactions: site-specific cleavage of two nucleotides from both 3' ends of viral DNA, and sequence-independent joining of the recessed viral ends to staggered phosphates in a target DNA. Here we investigate human immunodeficiency virus type 1 (HIV-1) IN-DNA interactions using surface plasmon resonance. The results show that IN forms tight complexes both with duplex oligonucleotides that represent the viral DNA ends and with duplex oligonucleotides with an unrelated sequence that represent a target DNA substrate. The IN-DNA complexes are stable in 4.0 M NaCl, or 50% (v/v) methanol, but they are not resistant to low concentrations of SDS, indicating that their stability is highly dependent on structural features of the protein. Divalent metal cofactors exert two distinct effects on the IN-DNA interaction. Mn2+ inhibits IN binding to a model target DNA with the apparent Kd increasing approximately 3-fold in the presence of this cation. On the other hand, Mn2+ (or Mg2+) stimulates the binding of IN to a model viral DNA end, decreasing the apparent Kd of this IN-viral DNA complex approximately 6-fold. Such metal-mediated stimulation of the binding of IN to the viral DNA is totally abolished by substitution of the subterminal conserved CA/GT bp with a GT/CA bp, and is greatly diminished when the viral DNA end is recessed or "pre-processed." IN binds to a viral duplex oligonucleotide whose end was extended with nonviral sequences with kinetics similar to the nonviral model target DNA. This suggests that IN can distinguish the integrated DNA product from the viral donor DNA in the presence of divalent metal ion. Thus, our results show that preferential recognition of viral DNA by HIV-1 IN is achieved only in the presence of metal cofactor, and requires a free, wild-type viral DNA end.