title: Phosphorylation decreases trypsin activation and apolipoprotein al binding to glycosylphosphatidylinositol-specific phospholipase D.
abstract: Glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) is present in plasma as an apolipoprotein and as a cell-associated lipase. GPI-PLD mRNA levels are regulated, but it is unclear if posttranslational mechanisms also regulate GPI-PLD function. We examined the effect of protein kinase A phosphorylation on human serum GPI-PLD activity, trypsin activation, and apolipoprotein AI binding. Protein kinase A phosphorylation did not activate GPI-PLD activity in vitro, nor did phosphorylated GPI-PLD cleave a GPI-anchored protein from intact porcine erythrocytes. Trypsin cleaves the C-terminal beta propeller of purified human serum GPI-PLD to generate three immunodetectable fragments (75, 28, and 18 kDa) in association with a 12-fold increase in enzyme activity. After phosphorylation, the amounts of 28- and 18-kDa fragments were markedly decreased with trypsin treatment, and activity was only increased five-fold. Phosphorylation also inhibits binding of GPI-PLD to apolipoprotein AI. These data are the first demonstrating that phosphorylation may regulate GPI-PLD interaction with other proteins.
authors: Department of Medicine, Indiana University School of Medicine and the Department of Veterans Affairs, Indianapolis 46202, USA. mdeeg@iupui.edu
authors: Mark A
authors: MA
authors: Deeg
authors: Rosario F
authors: RF
authors: Bowen
mesh_terms: D000704:Analysis of Variance; D016632:Apolipoprotein A-I / Q000097:blood / Q000378:metabolism*; D001665:Binding Sites; D015153:Blotting, Western; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D006801:Humans; D017830:Octoxynol; D010739:Phospholipase D / Q000097:blood / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation; D011092:Polyethylene Glycols; D011499:Protein Processing, Post-Translational; D011869:Radioligand Assay; D014357:Trypsin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D016632:Apolipoprotein A-I; D011092:Polyethylene Glycols; D017830:Octoxynol; C010615:Nonidet P-40; D017868:Cyclic AMP-Dependent Protein Kinases; D010739:Phospholipase D; C065017:glycoprotein phospholipase D; D014357:Trypsin