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Figure 2<br />

Schematic representation of the specificity subsites of the HIV PR active site with bound<br />

peptidic inhibitor JG-365. Amino acids forming the boundaries of the particular<br />

subsites are shown.<br />

the hydrogen bond donor and acceptor functional groups of the active site are located in an approximate<br />

plane that lies along the long axis of the tunnel and is somewhat perpendicular to the plane of the<br />

subsites. The hydrogen-bonding functionalities include the carboxylates of the catalytic aspartates, the<br />

carbonyl oxygens of Gly27 and Gly48, the amide nitrogens of Asp29' and Gly48, the carboxylate of<br />

Asp29', and the dimer symmetry-related groups on the other side of the active site. Additional groups<br />

capable of forming hydrogen bonds with ligands are located in the outer part of the S2/S2' subsite and<br />

include the amide nitrogens and the carboxylates of Asp30/30'. There are five conserved water<br />

molecules in the active site of HIV PR. Four of the waters are symmetrically distributed in the S3/S3'<br />

subsites and one, hereafter called Wat301, is located near the two-fold axis of the dimer and, in the<br />

presence of most inhibitors, is approximately tetrahedrally coordinated <strong>by</strong> the hydrogen bonds formed<br />

between carbonyl oxygens of the ligand(s) and the amide nitrogens of Ile50/50' of the flaps. In the<br />

ligand-bound form of HIV PR, Wat301 is completely inaccessible to solvent, and it has been speculated<br />

that its functional substitution could be energetically favorable [18] or at least may lead to discovery of<br />

novel nonpeptidic inhibitors [20]. Thus, there are 18 hydrogen bond donors or acceptors in<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_6.html [2/29/2004 2:15:34 AM]<br />

Page 6

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