Phosphatidylethanolamine - Wikipedia
In this report, we describe a new approach for the production of lipid antigens that elicit specific immune responses against phosphatidylserine (PS). Because phospholipids are small nonimmunogenic haptens, PS analogs containing activated coupling groups were synthesized and covalently attached to carrier proteins. Sulfhydryl-reactive PS was generated by acylation of 1-oleoyl-2-(aminocaproyl)phosphatidylcholine with N-succinimidyl-3-(2-pyridyldithio) propionate, converted to PS by phospholipase D-catalyzed base exchange with L-serine, and conjugated to carrier proteins by thiol-disulfide exchange. Antisera to these lipid hapten-protein carrier conjugates were developed in rabbits. Antibodies bound PS but not phosphatidylcholine (PC), phosphatidylglycerol, phosphatidic acid, or phosphatidylethanolamine (PE) when presented together with PC. Inhibition studies using watersoluble lipid analogs and sonicated vesicles indicated that antibody specificity was directed toward the lipid's polar head group. These antibodies also inhibited the PS-dependent prothrombinase activity assay by ~60%. These data show that the covalent coupling of phospholipid haptens to protein carriers via the lipid's fatty acyl side chains preserves its primary head group moiety for the production of specific lipid antibodies.
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AB - The adducts that form when aldehydes modify proteins have been implicated in the pathogenesis of vascular disease and aging. Our previous studies indicated that p-hydroxyphenylacetaldehyde (pHA), the major product of L-tyrosine oxidation by the myeloperoxidase/hydrogen peroxide/chloride system of phagocytes, covalently modifies the ε-amino group of lysine residues at sites of inflammation. Here, we report that pHA also reacts with the amino group of synthetic phospholipids and red blood cell model systems. Using fast atom bombardment mass spectrometric analysis of ethanolamine glycerophospholipid or serine glycerophospholipid incubated with pHA and NaBH3CN, we detected products that were consistent with reduced phospholipid Schiff base adducts. We confirmed the reaction of the aldehyde with the amino group through 1H NMR and mass spectrometric analysis of polar headgroups recovered from the modified and reduced parent lipid. When phospholipid model systems and cell membranes were exposed to physiological levels of L-tyrosine and the myeloperoxidase/hydrogen peroxide/chloride system followed by treatment with NaBH3CN, reduced Schiff base adducts of pHA with ethanolamine glycerophospholipid and serine glycerophospholipid (pHA-PE and pHA-PS, respectively) were produced. The reaction required myeloperoxidase, hydrogen peroxide, L-tyrosine, and chloride ion; it was inhibited by catalase or heme poisons, implicating hydrogen peroxide and peroxidase in the pathway. Collectively, these results demonstrate that an aldehyde generated by the myeloperoxidase system of phagocytes can covalently modify the amino groups of phosphatidylethanolamine and phosphatidylserine. Because amino glycerophospholipids are critical components of cell membranes and circulating lipoproteins such as LDL, similar reactions may play important roles in the initiation or progression of disease at sites of inflammation.
Simple sulfonamide and amide derivatives of tris(2-aminoethyl)amine (Tren) are known to promote the translocation or flip-flop of phosphatidylcholine, but not phosphatidylserine, across bilayer membranes. This paper describes the synthesis of a 300-member, spatially encoded library of Tren derivatives with appended peptide−sulfonamide and peptide−urea arms. The library was synthesized using the Encore method with SynPhase lanterns as the solid support. A high-throughput assay was developed to screen individual members of the library for an ability to translocate a fluorescent NBD derivative of phosphatidylserine across vesicle membranes. Several lead compounds were identified, and one was synthesized independently to confirm its high phosphatidylserine translocation activity.