PORCINE PANCREATIC ELASTASE COMPLEXED WITH (3S, 4S)N-PARA-TOLUENESULPHONYL -3-ETHYL-4-(CARBOXYLIC ACID)PYRROLIDIN-2-ONE SOAKED IN PH 9 BUFFER FOR TWO MINUTES
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 ...
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.
Related Citations:
Mechanistic Insights Into the Inhibition of Serine Proteases by Monocyclic Lactams Wilmouth, R.C., Kassamally, S., Westwood, N.J., Sheppard, R.J., Claridge, T.D.W., Aplin, R.T., Wright, P.A., Pritchard, G.J., Schofield, C.J. (1999) Biochemistry 38: 7989
Inhibition of Elastase by N-Sulfonylaryl Beta-Lactams: Anatomy of a Stable Acyl-Enzyme Complex Wilmouth, R.C., Westwood, N.J., Anderson, K., Brownlee, W., Claridge, T.D.W., Clifton, I.J., Pritchard, G.J., Aplin, R.T., Schofield, C.J. (1998) Biochemistry 37: 17506
Structure of a Specific Acyl-Enzyme Complex Formed between Beta-Casomorphin-7 and Porcine Pancreatic Elastase Wilmouth, R.C., Clifton, I.J., Robinson, C.V., Roach, P.L., Aplin, R.T., Westwood, N.J., Hajdu, J., Schofield, C.J. (1997) Nat Struct Biol 4: 456
Structure of Native Porcine Pancreatic Elastase at 1.65 A Resolution Meyer, E., Cole, G., Radhakrishnan, R., Epp, O. (1988) Acta Crystallogr B 44: 26
Organizational Affiliation:
The Oxford Centre for Molecular Sciences and The Dyson Perrins Laboratory, South Parks Road, Oxford OX1 3QY, UK.
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