Condensing and Fluidizing Effects of Ganglioside GM1 on Phospholipid Films

Abstract

Mixed monolayers of the ganglioside G(M1) and the lipid dipalmitoylphosphatidlycholine (DPPC) at air-water and solid-air interfaces were investigated using various biophysical techniques to ascertain the location and phase behavior of the ganglioside molecules in a mixed membrane. The effects induced by G(M1) on the mean molecular area of the binary mixtures and the phase behavior of DPPC were followed for G(M1) concentrations ranging from 5 to 70 mol %. Surface pressure isotherms and fluorescence microscopy imaging of domain formation indicate that at low concentrations of G(M1) (<25 mol %), the monolayer becomes continually more condensed than DPPC upon further addition of ganglioside. At higher G(M1) concentrations (>25 mol %), the mixed monolayer becomes more expanded or fluid-like. After deposition onto a solid substrate, atomic force microscopy imaging of these lipid monolayers showed that G(M1) and DPPC pack cooperatively in the condensed phase domain to form geometrically packed complexes that are more ordered than either individual component as evidenced by a more extended total height of the complex arising from a well-packed hydrocarbon tail region. Grazing incidence x-ray diffraction on the DPPC/G(M1) binary mixture provides evidence that ordering can emerge when two otherwise fluid components are mixed together. The addition of G(M1) to DPPC gives rise to a unit cell that differs from that of a pure DPPC monolayer. To determine the region of the G(M1) molecule that interacts with the DPPC molecule and causes condensation and subsequent expansion of the monolayer, surface pressure isotherms were obtained with molecules modeling the backbone or headgroup portions of the G(M1) molecule. The observed concentration-dependent condensing and fluidizing effects are specific to the rigid, sugar headgroup portion of the G(M1) molecule.

Carbohydrate Conformation and Lipid Condensation in Monolayers Containing Glycosphingolipid Gb3: Influence of Acyl Chain Structure

“…Three repeat measurements were performed and variation in the APM was in the range of 5-10%. Consistent with isotherms of other GSL monolayers, the Gb3 isotherm showed changes to p at APM >80 Å 2 (18)(19)(20). The long-range interactions can be attributed to the carbohydrate hydration shell and following compression the APM converged to 40-50 Å 2 consistent with PC lipids (21,22).…”

Effects of Fullerenes on Phospholipid Membranes: A Langmuir Monolayer Study

“…For instance, the lipid monolayer model has been suggested to be suitable for characterizing protein-membrane interactions. [20] Miscibility of the mixed monolayers investigated here was evaluated on the basis of the excess areas of mixing A exc , calculated according to Equation (2) at various surface pressures [24,34] …”

Lateral stress relaxation and collapse in lipid monolayers

“…The condensed phase has a crystalline lattice structure that excludes the bulky Texas Red probe making this phase appear dark in comparison with the LE. 38,39 Fig. 2 and 3 show fluorescence images of the four systems at several different surface pressures.…”

“…When a biphasic (LE/C) single-component monolayer is deposited onto mica, the condensed domains are ∼0.7-0.9 nm taller than fluid lipids due to the difference in packing and tilt of the acyl chains. 39,41 Since all monolayers examined in this paper are phase-separated at surface pressures of deposition, the height of numerous condensed domains can be used as a reference state. Any material that is lower in height than the C phase is more disordered in the monolayer.…”