Heparin prevents the binding of phospholipase A2 to phospholipid micelles: importance of the amino-terminus

The activity of the major isoform of porcine pancreatic phospholipase A2 (PLA2), designated B-PLA2, against micellar substrates is inhibited by heparin. Inhibition is a consequence of binding of the enzyme to heparin, documented by a heparin-induced alteration in the intrinsic fluorescence of B-PLA2...

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Bibliographic Details
Published in:	Biochemistry (Easton) Vol. 30; no. 37; pp. 9090 - 9097
Main Authors:	Dicciaani, Mitchell B, Lilly-Stauderman, Martha, McLean, Larry R, Balasubramaniam, Ambikaipakan, Harmony, Judith A. K
Format:	Journal Article
Language:	English
Published:	Washington, DC American Chemical Society 01-09-1991
Subjects:	Amino Acid Sequence Analytical, structural and metabolic biochemistry Animals Binding Sites - drug effects Biological and medical sciences Catalysis Drug Interactions Enzymes and enzyme inhibitors Fundamental and applied biological sciences. Psychology Heparin - pharmacology Hydrolases Hydrolysis Isoenzymes - antagonists & inhibitors Isoenzymes - chemistry Isoenzymes - drug effects Micelles Molecular Sequence Data Phospholipases A - antagonists & inhibitors Phospholipases A - chemistry Phospholipases A - drug effects Phospholipases A2 Phospholipids - chemistry Protein Binding - drug effects Protein Conformation Solutions Structure-Activity Relationship Swine Chemical modification Enzyme Active site Inhibitor enzyme complex Heparin Inhibition Phospholipase A Fluorescence spectrometry Dose activity relation
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Summary:	The activity of the major isoform of porcine pancreatic phospholipase A2 (PLA2), designated B-PLA2, against micellar substrates is inhibited by heparin. Inhibition is a consequence of binding of the enzyme to heparin, documented by a heparin-induced alteration in the intrinsic fluorescence of B-PLA2 and in the 8-anilino-1-naphthalene sulfonate fluorescence and by the enhanced rate of chemical modification of the active site residue His-48. As a consequence of heparin binding, the conformation of B-PLA2 at the active site and at the amino-terminus is altered, and the enzyme does not bind to phospholipid micelles. In spite of the heparin-induced conformational changes, B-PLA2 retains its ability to catalyze the hydrolysis of monomeric phospholipid. Other glycosaminoglycans can bind to and inhibit the activity of B-PLA2 toward organized phospholipids, but none tested is as effective as heparin. An isoform of the pancreatic enzyme, designated UB-PLA2 and which corresponds to iso-pig PLA2, does not bind to nor is its catalytic activity influenced by heparin. A peptide corresponding to the amino-terminal 26 residues of B-PLA2 can rescue PLA2 from heparin inhibition. A similar peptide corresponding to the amino-terminus of UB-PLA2 has no effect on heparin inhibition. A model for the inhibition of B-PLA2 by heparin is proposed in which the catalytically significant effect of heparin is to interact directly with the amino-terminus of B-PLA2, the interfacial recognition site, to prevent the enzyme from binding to micellar substrates.
Bibliography:	ark:/67375/TPS-0QKZD58F-N istex:807A861371543AFE5E696656602FFC836227C0D3
ISSN:	0006-2960 1520-4995
DOI:	10.1021/bi00101a026