Abstract
The thermotropic behavior of the natural glycosphingolipids galactosylceramide, asialo-Gal beta 1-3GalNAc beta 1-4Gal(3-2 alpha NeuAc)beta 1-4Glc beta 1-Cer (GM1), sulfatide, GM1, NeuAc alpha 2-3Gal beta 1-3GalNAc beta 1-4Gal(3-2 alpha NeuAc)beta 1-4Glc beta 1-1Cer (GD1a), and NeuAc alpha 2-3Gal beta 1-3GalNAc beta 1-4Gal(3-2 alpha NeuAc8-2 alpha NeuAc)beta 1-4Glc beta 1-1 Cer (GT1b), and their mixtures with dipalmitoylphosphatidylcholine (DPPC) in the presence of myelin basic protein (MBP) was studied by high sensitivity differential scanning calorimetry. The transition temperature of DPPC, galactosylceramide, and asialo-GM1 is affected little by MBP while their transition enthalpy is decreased in proportion to the amount of protein in the mixture. The thermotropic behavior of anionic glycosphingolipids is considerably perturbed by MBP. The transition temperature of gangliosides increases in the presence of MBP, whereas that of sulfatide decreases. The enthalpy of the transition of anionic glycosphingolipids increases markedly in the presence of MBP. The excess heat capacity function of these systems can be resolved into two independent phase transitions. Phase separation of enriched lipid/protein domains occurs in a magnitude that depends on the amount of MBP; the rest of the lipid phase exhibits some altered thermodynamic properties. In mixtures of glycosphingolipids with DPPC, phase separation is also present but no phase transition with the characteristic of pure DPPC is found. MBP is changing the properties of the lipid mixture as a whole and does not interact exclusively with the glycosphingolipids. The proportion of MBP required to produce the maximal changes is greater the greater the complexity of the glycosphingolipids polar head group. Relatively small variations of the amount of MBP induce large shifts in the proportion of the different phases present.
Highlights
From the Department of Neurology, Yale University School of Medicine and Departmentof Chemistry, Yale University, New Haven, Connecticut 06510
The transition temperature of DPPC,galactosylceramide,and asialo-GM1is affected little by myelin basic protein (MBP) while their transitionenthalpy is decreased in proportiontothe andinterfacial behaviorinmonolayers (3).The molecular parameters derived from the study of the behavior of glycosphingolipids in monolayers can be used to extend the description and predict some properties of three-dimensional aggregates (4)
The enthalpy of the tran- It was previously shown that myelin basic protein (MBP) is sition of anionic glycosphingolipids increases mark- able to penetrate into monolayers of neutral glycosphingoedly in the presencoef MBP
Summary
Glycosphingolipids show considerable interactions withdifamount of protein in the mixture. The transition temperaturoef gan- resulting lipid/protein mixture insonideal, and themolecular gliosides increases in the presence of MBP, whereas properties of the individual components are modified (5-7). Some of depends on the amount of MBP; the rest of the lipid theseinteractionsare thermodynamicallyfavored, and the phase exhibits some altered thermodynamic proper- amount of protein that can be present in a homogeneously ties. MBP is phaseseparation of protein-enrichedand lipid-enriched changing the propertieosf the lipid mixture as a whole phases occurs (7). The thermotropicbehavior of dilute aqueous dispersions of individual glycosphingolipids and the phase diagramovser the tein asbelonging to group 11. This group is thought to interact with lipids by a combination of electrostatic andhydrophobic forces.
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