1e37: Difference between revisions

beta-Lactams inhibit a range of enzymes via acylation of nucleophilic, serine residues. Certain gamma-lactam analogues of monocyclic beta-lactams, have also been shown to be reversible inhibitors of porcine pancreatic, elastase (PPE), forming acyl-enzyme complexes that are stable with respect, to hydrolysis. Crystallographic analysis at pH 5 of an acyl-enzyme complex, formed with PPE and one of these inhibitors revealed the ester carbonyl, located in the oxyanion hole in a similar conformation to that observed in, the structure of a complex formed between a heptapeptide, (beta-casomorphin-7) and PPE. Only weak electron density was observed for, the His-57 side chain in its 'native' conformation. Instead, the His-57, side chain predominantly adopted a conformation rotated approx. 90 degrees, from its normal position. PPE-gamma-lactam crystals were subjected to, 'pH-jumps' by placing the crystals in a buffer of increased pH prior to, freezing for data collection. The results indicate that the conformation, of the gamma-lactam-derived acyl-enzyme species in the PPE active site is, dependent on pH, a result having implications for the analysis of other, serine protease-inhibitor structures at non-catalytic pH values. The, results help to define the stereoelectronic relationship between the ester, of the acyl-enzyme complex, the side chain of His-57 and the incoming, nucleophile during the reversible (de)acylation steps, implying it is, closely analogous to the hydrolytic deacylation step during catalytic, peptide hydrolysis.

1E37 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 CA, SO4 and TPY 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] Structure known Active Site: CAT. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1E37 OCA].  

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