8est: Difference between revisions

[[Image:8est.gif|left|200px]]<br /><applet load="8est" size="350" color="white" frame="true" align="right" spinBox="true"  

The crystal structure of the acyl enzyme formed upon inhibition of porcine pancreatic elastase (PPE) by 4-chloro-3-ethoxy-7-guanidinoisocoumarin has been determined at a 1.85-A effective resolution. The chlorine atom is still present in this acyl enzyme, in contrast to the previously reported structure of the 7-amino-4-chloro-3-methoxyisocoumarin-PPE complex where the chlorine atom has been replaced by an acetoxy group. The guanidino group forms hydrogen bonds with the carbonyl group and side-chain hydroxyl group of Thr-41, and the acyl carbonyl group has been twisted out of the oxyanion hole. Molecular modeling indicates that the orientation of the initial Michaelis enzyme-inhibitor complex is quite different from that of the acyl enzyme since simple reconstruction of the isocoumarin ring would result in unfavorable interactions with Ser-195 and His-57. Molecular models were used to design a series of new 7-(alkylureido)- and 7-(alkylthioureido)-substituted derivatives of 3-alkoxy-7-amino-4-chloroisocoumarin as PPE inhibitors. All the 3-ethoxyisocoumarins were better inhibitors than those in the 3-methoxy series due to better interactions with the S1 pocket of PPE. The best ureido inhibitor also contained a tert-butylureido group at the 7-position of the isocoumarin. Due to a predicted interaction with a small hydrophobic pocket on the surface of PPE, this isocoumarin and a related phenylthioureido derivative are among the best irreversible inhibitors thus far reported for PPE (kobs/[I] = 8100 M-1 s-1 and 12,000 M-1 s-1). Kinetic studies of the stability of enzyme-inhibitor complexes suggest that many isocoumarins are alkylating the active site histidine at pH 7.5 via a quinone imine methide intermediate, while at pH 5.0, the predominant pathway appears to be simple formation of a stable acyl enzyme derivative.

8EST is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Sus_scrofa Sus scrofa] with <scene name='pdbligand=SO4:'>SO4</scene>, <scene name='pdbligand=CA:'>CA</scene> and <scene name='pdbligand=GIS:'>GIS</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Pancreatic_elastase Pancreatic elastase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.4.21.36 3.4.21.36] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=8EST OCA].  

[[Category: Meyerjunior, E F.]]

[[Category: Powers, J C.]]

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