title: Targeting of porcine pancreatic phospholipase A2 to human platelets: introduction of an RGD sequence by genetic engineering.
abstract: The possibility to induce specific disruption of activated platelets by binding of porcine pancreatic phospholipase A2 (PLA2) was tested by constructing a set of PLA2-mutants containing an Arg-Gly-Asp (RGD) sequence. One mutant was made with RGD as part of a surface-exposed loop (RGDloop). Four mutants were made with RGD as part of a C-terminal extension: one with RGD directly coupled to the C-terminus (RGDc) and three mutants (CRSx) with x= 22, 42 and 82 hydrophylic non-charged amino acids between RGD and the enzyme. All mutants retained 20-80% activity of native PLA2 and showed little binding to resting platelets. The binding of the native enzyme and RGDloop was not increased following stimulation. In contrast, the mutants RGDc and CRSx showed stimulation-dependent binding to the platelet receptor GPIIb/IIIa, since GRGDS-peptide and a monoclonal antibody against the complex interfered with binding. In alpha-thrombin-stimulated platelets, CRS42 and CRS82 induced about 5% hydrolysis of [3H]-arachidonic acid-labeled phospholipids. Stimulation with a combination of alpha-thrombin and collagen (known to expose phosphatidylserine) increased hydrolysis to 11%. Despite the membrane disruption, the cells did not leak lactate dehydrogenase. We conclude that PLA2 can be targeted to activated platelets by introducing RGD in a C-terminal extension with a minimum distance (42 amino acids) between RGD and the enzyme. However, more hydrolytic activity is required to eliminate activated platelets among a suspension of resting platelets and other blood cells.
authors.affiliation: Department of Haematology, University Hospital Utrecht, The Netherlands.
authors.forename: A C
authors.initials: AC
authors.lastname: Bekkers
authors.forename: H
authors.initials: H
authors.lastname: van der Vuurst
authors.forename: G
authors.initials: G
authors.lastname: van Willigen
authors.forename: J W
authors.initials: JW
authors.lastname: Akkerman
authors.forename: H M
authors.initials: HM
authors.lastname: Verheij
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016503:Drug Delivery Systems; D005818:Genetic Engineering; D006801:Humans; D008969:Molecular Sequence Data; D010741:Phospholipases A / Q000008:administration & dosage* / Q000235:genetics* / Q000378:metabolism; D054467:Phospholipases A2; D015539:Platelet Activation / Q000187:drug effects*; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism; D013552:Swine
chemical_list: D011994:Recombinant Proteins; D010741:Phospholipases A; D054467:Phospholipases A2