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Figure 6<br />

Molscript stereo figure of the three-dimensional structure of the catalytic core of<br />

HIV-1 integrase. The two catalytically essential aspartic acid residues (D64 and D116)<br />

visible in the x-ray structure are highlighted.<br />

Page 94<br />

an α-β meander sandwich (see Figure 6) [35]. In the crystal structure, interpretable electron density<br />

starts at Cys56, leading to a short loop. The first β strand starts at Gly59 and runs until Val68. The two<br />

central residues of a type I' reverse β turn, Glu69 and Gly70, change the polypeptide chain direction to<br />

form the second β strand between residues Lys71 and His78, which runs antiparallel with the first<br />

strand. A type I'β turn follows, with Val79 and Ala80 changing the chain direction again to form the<br />

third β strand between Ser81 and Ile89, which runs antiparallel with the second strand. A short loop<br />

between Pro90 and Glu92 leads to the first α helix (helix A) between Thr93 and Trp108. This helix<br />

packs against the bottom face of the sheet formed <strong>by</strong> the first three antiparallel strands <strong>by</strong> several<br />

hydrophobic interactions. A short loop (Pro109 and Val110) leads to the fourth β strand between Lys111<br />

and His114. This strand is parallel with the first. A short loop starting at Thr115 leads to helix B, a one<br />

turn helix between Gly118 and Thr122, followed <strong>by</strong> helix C between Ser123 and Ala133. This helix<br />

runs parallel to and packs against helix A. The residues Gly134 and Ile135 form a short loop prior to the<br />

fifth and last β strand of the structure between Lys136 and Ala138. This short strand is parallel with the<br />

first and the fourth. There is no interpretable electron density due to disorder between Gly140 and<br />

Met154. At Met154, the fourth α helix (helix D) starts and runs until Ala169 on the top face of the sheet<br />

formed <strong>by</strong> the first three β strands. The residue Glu170 leads into the next helix (helix E) running<br />

between His171 and Lys186, the first residue of a short basic sequence (Lys186, Arg187, and Lys188).<br />

Together with<br />

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