Conformational studies of sphingolipids by NMR spectroscopy. I. Dihydrosphingonmyelin

The conformational features of dihydrosphingomyelin (DHSM), the major phosp holipid of human lens membranes, were investigated by H-1 and P-31 nuclear magnetic resonance spectroscopy. Several postulates emerge from the observe d trends: (a) in partially hydrated samples of DHSM in CDCl3 above 13 mM, a t which lipid-lipid interactions prevail, the amide proton is mostly involv ed in intermolecular H-bonds that link neighboring phospholipids through br idging water molecules. In the absence of water, the NH group is involved i n an intramolecular H-bond that restricts the mobility of the phosphate gro up. (b) In the monomeric form of the lipid molecule, the amide proton of th e major conformer is bound intramolecularly with one of the anionic and/or ester oxygens of the phosphate group. A minor conformer may also be present in which the NH proton participates in an intramolecular H-bond linking to the OH group of the sphingoid base. (c) Complete hydration leads to an ext ension of the head group as water molecules bind to the phosphate and NH gr oups via H-bonds, thus disrupting the intramolecular H-bonds prevalent at l ow concentrations. (C) 2000 Elsevier Science B.V. All rights reserved.