Physicochemical properties of the mouse plasmacytoma cell membranes with modified phospholipids

Earlier work from our laboratory has demonstrated that the modification of membrane phospholipid composition markedly retards secretion of immunoglobulin G1 by mouse plasmacytoma MOPC-31C cells. In the present study, we examined the physicochemical properties of lipid vesicles prepared from these cells with modified phospholipids by analyzing temperature dependence of 1H NMR signal line-widths of fatty-acyl chains. The results suggest that the export of IgG1 is affected by the local microenvironment of membranes rather than the bulk fluidity.     

Complex formation of peptide antibiotic Ro09-0198 with lysophosphatidylethanolamine: 1H NMR analyses in dimethyl sulfoxide solution

Ro09-0198 is a peptide antibiotic and immunopotentiator produced by Streptoverticillium griseoverticillatum which exhibits antitumor and antimicrobial activities. The chemical structure has been determined [Kessler et al. (1988) Helv. Chim. Acta 71, 1924-1929; Wakamiya et al. (1988) Tetrahedron Lett. 37, 4771-4772]. This peptide specifically interacts with (lyso)phosphatidylethanolamine, causing hemolysis and enhancing permeability in phosphatidylethanolamine-containing vesicles [Choung et al. (1988) Biochim. Biophys. Acta 940, 171-179, 180-187]. The highly specific nature of the interaction was studied by two dimensional proton NMR analyses. Proton resonances of the peptide were observed in dimethyl sulfoxide solution in the presence of 1-dodecanoyl-sn-glycerophosphoethanolamine. By comparison to the chemical shifts in the absence of lysophosphatidylethanolamine and by analysis of intermolecular cross-peaks in NOESY spectra, amino acid residues involved in the binding with the phospholipid were identified. The ammonium group of the phospholipid interacts with the carboxylate group of beta-hydroxyaspartic acid-15 but not with that of the carboxylate terminus. The secondary ammonium group of lysinoalanine-19/6 is probably bound to the phosphate group of the lipid. The peptide does not interact strongly with the fatty acid chain of the lipid. A folded structure of the central part [from Phe7 to Ala(S)14] of the peptide opens on binding with the phospholipid and accommodates the glycerophosphoethanolamine head group.     

Nuclear magnetic resonance analyses of side chain conformations of histidine and aromatic amino acid derivatives. Solvent and pH dependence

Stereoselectively beta-deuterated species were synthesized of Ac-His-NHMe, Ac-His-OEt, Ac-His-OH and H-His-NHMe, which are useful as models of histidine residues in peptides. From the spectral comparison of 1H n.m.r., the beta-proton resonances of the normal species were unambiguously assigned. In (C2H3)2SO, C2(2)H5O2H, C2H3O2H, and C5(2)H5N solution and in aqueous solution, the lower-field and higher-field components of beta-proton resonances of the four histidine derivatives are assigned to the pro-R and pro-S protons, respectively. The alternative assignments apply for Ac-His-NHMe, Ac-His-OEt and Ac-His-OH in non-polar solvents such as C2HCl3. Vicinal coupling constants 3J alpha beta S and 3J alpha beta R were obtained for calculating the fractional populations of rotamers about the C alpha-C beta bond. The rotamer populations depend little on the ionization states of the alpha-amino and carboxyl groups or the imidazole ring. The rotamer populations depend significantly on the solvent polarity, similar to those of Phe, Tyr and Trp derivatives. For the two beta-proton resonances of His, Phe, Tyr, and Trp derivatives in a variety of solvents, linear relationships are found between the differences in chemical shifts and the differences in vicinal coupling constants.