Docosahexaenoic acid-containing phosphatidylcholine affects the binding of monoclonal antibodies to purified Kb reconstituted into liposomes.
Class I major histocompatibility complex (MHC I) molecules are transmembrane proteins that bind and present peptides to T-cell antigen receptors. The role of membrane lipids in controlling MHC I structure and function is not understood, although membrane lipid composition influences cell surface expression of MHC I. We reconstituted liposomes with purified MHC I (Kb) and probed the effect of lipid composition on MHC I structure (monoclonal anti-MHC I antibody binding). Four phospholipids were compared; each had a phosphocholine head group, stearic acid in the sn-1 position, and either oleic, alpha-linolenic, arachidonic, or docosahexaenoic acid (DHA) in the sn-2 position. The greatest binding of monoclonal antibody AF6-88.5, which detects a conformationally sensitive epitope in the extracellular region of the MHC I alpha-chain, was achieved with DHA-containing proteoliposomes. Other epitopes (CTKb, 5041.16.1) showed some sensitivity to lipid composition. The addition of beta2-microglobulin, which associates non-covalently with the alpha-chain and prevents alpha-chain aggregation, did not equalize antibody binding to proteoliposomes of different lipid composition, suggesting that free alpha-chain aggregation was not responsible for disparate antibody binding. Thus, DHA-containing membrane lipids may facilitate conformational change in the extracellular domains of the alpha-chain, thereby modulating MHC I function through effects on that protein's structure.
Jenski
L J
LJ
Department of Biology, Indiana University-Purdue University at Indianapolis, 46202-5132, USA. ljenski@iupui.edu
Nanda
P K
PK
Jiricko
P
P
Stillwell
W
W
D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism*; D017951:Antigen Presentation; D002460:Cell Line; D004281:Docosahexaenoic Acids; D000939:Epitopes / Q000737:chemistry / Q000378:metabolism; D006183:H-2 Antigens / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008081:Liposomes / Q000737:chemistry*; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D010713:Phosphatidylcholines; D011485:Protein Binding; D011487:Protein Conformation; D011510:Proteolipids / Q000737:chemistry; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D001613:beta 2-Microglobulin / Q000378:metabolism
D000911:Antibodies, Monoclonal; D000939:Epitopes; D006183:H-2 Antigens; C032876:H-2Kb protein, mouse; D008081:Liposomes; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D011510:Proteolipids; D001613:beta 2-Microglobulin; C020485:proteoliposomes; D004281:Docosahexaenoic Acids