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Figure 1<br />

Stereo view of the α-carbon backbone of HIV PR dimer. (a) The apoenzyme<br />

with flaps in the “open” conformation. (b) Inhibited form of HIV PR with flaps in a<br />

“closed” conformation. For clarity, the inhibitor is removed from the active site.<br />

pepsin-like aspartic protease and consists of antiparallel β-strands and a short, two-turn α-helix<br />

connected <strong>by</strong> loops of varying length. The dimer interface is formed <strong>by</strong> an antiparallel β-sheet<br />

comprising two strands from each monomer. The hydrophobic residues from those β-strands and two<br />

symmetry-related α-helices form the core of the dimer. The dimer is further stabilized <strong>by</strong> a net of<br />

hydrogen bonds involving the residues around the catalytic aspartic acids. The active site is formed <strong>by</strong><br />

the dimer interface and is composed of equivalent contributions of residues from each monomer. The<br />

substrate-binding cleft is bound on one side <strong>by</strong> the active site aspartic acid (Asp25/25') and on the other<br />

side <strong>by</strong> a pair of two-fold related, antiparallel β-hairpin structures, commonly referred to as “flaps.”<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_4.html [2/29/2004 2:15:23 AM]<br />

Page 4

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