title: Highly selective hydrolysis of fatty acyl-CoAs by calcium-independent phospholipase A2beta. Enzyme autoacylation and acyl-CoA-mediated reversal of calmodulin inhibition of phospholipase A2 activity.
abstract: Calcium-independent phospholipase A2beta (iPLA2beta) participates in numerous diverse cellular processes, such as arachidonic acid release, insulin secretion, calcium signaling, and apoptosis. Herein, we demonstrate the highly selective iPLA2beta-catalyzed hydrolysis of saturated long-chain fatty acyl-CoAs (palmitoyl-CoA approximately myristoyl-CoA >> stearoyl-CoA >> oleoyl-CoA approximately = arachidonoyl-CoA) present either as monomers in solution or guests in host membrane bilayers. Site-directed mutagenesis of the iPLA2beta catalytic serine (S465A) completely abolished acyl-CoA thioesterase activity, demonstrating that Ser-465 catalyzes both phospholipid and acyl-CoA hydrolysis. Remarkably, incubation of iPLA2beta with oleoyl-CoA, but not other long-chain acyl-CoAs, resulted in robust stoichiometric covalent acylation of the enzyme. Moreover, S465A mutagenesis or pretreatment of wild-type iPLA2beta with (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one unexpectedly increased acylation of the enzyme, indicating the presence of a second reactive nucleophilic residue that participates in the formation of the fatty acyl-iPLA2beta adduct. Radiolabeling of intact Sf9 cells expressing iPLA2beta with [3H]oleic acid demonstrated oleoylation of the membrane-associated enzyme. Partial trypsinolysis of oleoylated iPLA2beta and matrix-assisted laser desorption ionization mass spectrometry analysis localized the acylation site to a hydrophobic 25-kDa fragment (residues approximately 400-600) spanning the active site to the calmodulin binding domain. Intriguingly, calmodulin-Ca2+ blocked acylation of iPLA2beta by oleoyl-CoA. Remarkably, the addition of low micromolar concentrations (5 microM) of oleoyl-CoA resulted in reversal of calmodulin-mediated inhibition of iPLA2 beta phospholipase A2 activity. These results collectively identify the molecular species-specific acyl-CoA thioesterase activity of iPLA2beta, demonstrate the presence of a second active site that mediates iPLA2beta autoacylation, and identify long-chain acyl-CoAs as potential candidates mediating calcium influx factor activity.
authors.affiliation: Division of Bioorganic Chemistry and Molecular Pharmacology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Jenkins
authors.forename: Wei
authors.initials: W
authors.lastname: Yan
authors.forename: David J
authors.initials: DJ
authors.lastname: Mancuso
authors.forename: Richard W
authors.initials: RW
authors.lastname: Gross
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism*; D000215:Acylation; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008051:Lipid Bilayers; D008823:Micelles; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010741:Phospholipases A / Q000235:genetics / Q000378:metabolism*; D054467:Phospholipases A2; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D018411:Spodoptera
chemical_list: D000214:Acyl Coenzyme A; D002147:Calmodulin; D008051:Lipid Bilayers; D008823:Micelles; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium