Refined solution structure of the dimeric N-terminal HHCC domain of HIV-2 integrase

The solution structure of the dimeric N-terminal domain of HIV-2 integrase (residues 1–55, named IN1−55) has been determined using NMR spectroscopy. The structure of the monomer, which was already reported previously [Eijkelenboom et al. (1997) Curr. Biol., 7, 739–746], consists of four α-helices and is well defined. Helices α1, α2 and α3 form a three-helix bundle that is stabilized by zinc binding to His12, His16, Cys40 and Cys43. The dimer interface is formed by the N-terminal tail and the first half of helix α3. The orientation of the two monomeric units with respect to each other shows considerable variation. 15N relaxation studies have been used to characterize the nature of the intermonomeric disorder. Comparison of the dimer interface with that of the well-defined dimer interface of HIV-1 IN1−55 shows that the latter is stabilized by additional hydrophobic interactions and a potential salt bridge. Similar interactions cannot be formed in HIV-2 IN1−55 [Cai et al. (1997) Nat. Struct. Biol., 4, 567–577], where the corresponding residues are positively charged and neutral ones.