Phospholipids enhance the binding of peptides to class II major histocompatibility molecules.

Abstract

The binding of a lysozyme and ovalbumin peptide to purified class II major histocompatibiity molecules in detergents was increased by the addition of certain lipids. Natural lipids from B lymphoma cells enhanced the binding and so did phosphatidylcholine, phosphatidylserine, phosphatidylinositol, and cardiolipin. Phosphatidylethanolamine, sphingomyelin, and cholesterol had no effect. There was no major difference between the effects of a phospholipid and its lyso derivative. As studied with phosphatidylcholine, the increase in peptide binding was also dependent on the fatty acid composition of the lipid. (MHC) proteins (1,2). The extent of binding of peptides to histocompatibility molecules, which can be studied in detergent solutions (1-7), usually correlates with their immunogenicity in vivo (2-4). There are, however, indications that the interactions of peptides with class II MHC may be quantitatively different on live antigen-presenting cells. For example, the binding of antigenic peptides to class II MHC molecules on live cells was reported to be much faster than that found in solution (8-10). A similar result was found for the dissociation of peptides bound to the class II MHC molecules (11).We recently found that the labeling of class II MHC molecules to peptides containing a photoreactive compound was influenced by phospholipids, both in the extent as well as in the relative degree ofthe a or p chain labeling (12). When tested on cell membranes that contained class II MHC proteins, photoreactive conjugates of the hen egg white lysozyme (HEL) peptide from residues 46 to 61 labeled exclusively the a chain of I-Ak (13). Conversely, I-Ak purified in an equimolar solution of MEGA 8 and MEGA 9 detergents was labeled to similar extent on both chains. However, the addition of certain lysophospholipids resulted in strong binding, with lysophosphatidylcholine predominantly labeling the a chain and lysophosphatidylserine labeling the ,B chain. We concluded that class II MHC molecules contained dialyzable components required for their binding integrity and that, most likely, these components were lipids.Lipid-protein interactions are of critical importance in maintaining the biological activity of a number of membrane proteins (for review, see refs. 14-16). These interactions may have different degrees of specificity and often induce conformational changes in the protein critical for their function (14,(17)(18)(19)(20)(21)(22). Lipids, by interacting directly with the MHC protein or by changing the structure ofthe detergent micelles, may induce conformational changes reflected in the distal binding site of the protein (23,24). Consistent with this hypothesis are the observations indicating that class II MHC molecules reconstituted in lipid monolayers present peptides differently, depending on the lipid composition (25). Other studies have shown that treatment of antigen-presenting cells with purified phospholipase A2 or C, or with cerulenin, an antibiotic that interferes with lipid metabolism, greatly dimi...

Ligand Exchange of Major Histocompatibility Complex Class II Proteins Is Triggered by H-bond Donor Groups of Small Molecules

“…The major goal of these attempts is to deliver high amounts of immunogenic peptide antigens derived from tumor-specific or tumor-associated proteins. In addition to the benefit of increased loading rates, these small molecular catalysts would also allow the bypassing of proteolytic endosomal processing compartments, which facilitates the presentation of epitopes sensitive to proteolytic degradation when following the classical MHC class II presentation pathway.Previous studies have already shown that, under certain conditions, the stability of peptide-MHC complexes can be affected by detergents or detergent-like compounds (16,17). The mechanism, however, remained obscure, and the chemical nature of these compounds did not allow any experiments with…”

“…Previous studies have already shown that, under certain conditions, the stability of peptide-MHC complexes can be affected by detergents or detergent-like compounds (16,17). The mechanism, however, remained obscure, and the chemical nature of these compounds did not allow any experiments with living cells.…”

Study of plasma-induced peripheral blood mononuclear cells survival using Fourier transform infrared microspectroscopy

“…32 Though cell division and proliferation was not affected as evaluated using the method proposed by Mourant et al, 33 increased survival indicated that AHP/NAHP influenced the metabolic pathways of PBMCs. We show that plasma factors influence the biogenesis of phospholipids (which are essential membrane components) that are required for normal functioning of APCs, as these are involved in processes like endocytosis, 39 autophagy, [40][41][42] and antigen processing and presentation. 43 Lipids are important components of lipid rafts that are essential for many cellular processes like transport and insertion of membrane proteins that can alter the structure and function of the immune cells and can lead to disease conditions.…”

Cellular mechanisms of antigen processing and the function of class I and II major histocompatibility complex molecules.

“…Different MHC alleles bind varying spectra of peptides, and a given peptide will generally bind only to a subset of MHC alleles. The presentation of and immune response to a peptide is, accordingly, "restricted" to these alleles, and this may explain the fact that increased risk of various autoimmune disorders is restricted to particular MHC genotypes Todd et al, 1988 (Roof et aL., 1990). Binding kinetics indicate that only 1 00/o-600/o of purified MHC-11 can bind peptides in vitro, a reflection of denaturation, occupation by other peptides, or the presence of different MHC-11 conformers that vary in their binding affinities.…”

“…Peptides bind to MHC-11 molecules in a saturable and homogeneous binding reaction with binding affinities in the micromolar range (Babbitt et aL, 1985). The binding is characterized by a slow on-rate and by a very slow rate of dissociation (Buus et al, 1986;Allen et al, 1989;SadeghNasseri and McConnell, 1989;Roof et al, 1990). Some peptides, once bound, will practically not dissociate unless the MHC-11 molecules are drastically denatured.…”