8est
From Proteopedia
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REACTION OF PORCINE PANCREATIC ELASTASE WITH 7-SUBSTITUTED 3-ALKOXY-4-CHLOROISOCOUMARINS: DESIGN OF POTENT INHIBITORS USING THE CRYSTAL STRUCTURE OF THE COMPLEX FORMED WITH 4-CHLORO-3-ETHOXY-7-GUANIDINO-ISOCOUMARIN
Overview
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previously reported, structure of the 7-amino-4-chloro-3-methoxyisocoumarin-PPE complex where, the chlorine atom has been replaced by an acetoxy group.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.
About this Structure
8EST is a Single protein structure of sequence from Sus scrofa with SO4, CA and GIS as ligands. Active as Pancreatic elastase, with EC number 3.4.21.36 Full crystallographic information is available from OCA.
Reference
Reaction of porcine pancreatic elastase with 7-substituted 3-alkoxy-4-chloroisocoumarins: design of potent inhibitors using the crystal structure of the complex formed with 4-chloro-3-ethoxy-7-guanidinoisocoumarin., Powers JC, Oleksyszyn J, Narasimhan SL, Kam CM, Biochemistry. 1990 Mar 27;29(12):3108-18. PMID:2337582
Page seeded by OCA on Tue Nov 20 15:10:36 2007
