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Figure 8<br />

Molscript stereo figure of the structure of the nonspecific DNA-binding domain<br />

of HIV-1 integrase, IN 220–270 , determined <strong>by</strong> heteronuclear NMR spectroscopy [28].<br />

Page 103<br />

The structure of this domain is of particular interest as it represents the dominant nonspecific DNAbinding<br />

region of integrase. Gel filtration and sedimentation equilibrium results indicated that purified<br />

IN 213–288 partitioned between dimers and highly aggregated material (unpublished observations).<br />

However, a smaller domain consisting of residues 220 to 270 maintains the DNA-binding properties of<br />

the longer C-terminal domain and is better behaved in solution. Recently, two groups have reported the<br />

structure of this smaller fragment, IN 220–270, determined using multidimensional heteronuclear NMR<br />

spectroscopic methods [28,29].<br />

As shown in Figure 8, the overall structure of IN 220–270, is that of a β sandwich formed <strong>by</strong> two threestranded<br />

β sheets. As anticipated <strong>by</strong> biophysical studies, the polypeptide is a dimer in solution. The<br />

interface between monomers is formed <strong>by</strong> the antiparallel interaction of three β strands from each<br />

subunit and is stabilized predominantly <strong>by</strong> hydrophobic interactions. There is a long loop between<br />

strands β1 and β2 which, in the dimer, defines the sides of a cleft that is of the appropriate dimensions<br />

(about 24 × 24 × 12 Å) to accommodate double-stranded DNA. The folding topology is very similar to<br />

that of SH3 domains that are found in several proteins involved in signal transduction, despite the lack<br />

of significant sequence homology. This is rather unusual since SH3 domains are generally involved in<br />

protein binding rather than interactions with DNA.<br />

V. Prospects for Inhibitors<br />

A. Overview of Inhibitor Studies to Date<br />

The investigation of HIV integrase inhibitors has been largely restricted to testing available compounds<br />

that inhibit other enzymes with similar substrates or<br />

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