The behavior of the two major galactolipids of wheat endosperm, mono- (MGDG) and di-galactosyldiacylglycerol (DGDG) was studied in aqueous dispersion and at the air/liquid interface. The acyl chains of the pure galactolipids and their binary equimolar mixture are in the fluid or liquid expanded phase. SAXS measurements on liquid-crystalline mesophases associated with the electron density reconstructions show that the DGDG adopts a lamellar phase L(alpha) with parallel orientation of the headgroups with respect to the plane of the bilayer, whereas MGDG forms an inverse hexagonal phase H(II) with a specific organization of galactosyl headgroups. The equimolar mixture shows a different behavior from those previously described with formation of an Im3m cubic phase. In comparing monolayers composed of the pure galactolipids and their equimolar mixtures, PM-IRRAS spectra show significant differences in the optical properties and orientation of galactosyl groups with respect to the interface. Furthermore, Raman and FTIR spectroscopies show that the acyl chains of the galactolipid mixture are more ordered compared to those of the pure components. These results suggest strong interactions between MGDG and DGDG galactosyl headgroups and these specific physical properties of galactolipids are discussed in relation to their biological interest in wheat seed.

Mycolactone is a lipid-like endotoxin synthesized by an environmental human pathogen, Mycobacterium ulcerans, the causal agent of Buruli ulcer disease. Mycolactone has pleiotropic effects on fundamental cellular processes (cell adhesion, cell death and inflammation). Various cellular targets of mycolactone have been identified and a literature survey revealed that most of these targets are membrane receptors residing in ordered plasma membrane nanodomains, within which their functionalities can be modulated. We investigated the capacity of mycolactone to interact with membranes, to evaluate its effects on membrane lipid organization following its diffusion across the cell membrane. We used Langmuir monolayers as a cell membrane model. Experiments were carried out with a lipid composition chosen to be as similar as possible to that of the plasma membrane. Mycolactone, which has surfactant properties, with an apparent saturation concentration of 1 μM, interacted with the membrane at very low concentrations (60 nM). The interaction of mycolactone with the membrane was mediated by the presence of cholesterol and, like detergents, mycolactone reshaped the membrane. In its monomeric form, this toxin modifies lipid segregation in the monolayer, strongly affecting the formation of ordered microdomains. These findings suggest that mycolactone disturbs lipid organization in the biological membranes it crosses, with potential effects on cell functions and signaling pathways. Microdomain remodeling may therefore underlie molecular events, accounting for the ability of mycolactone to attack multiple targets and providing new insight into a single unifying mechanism underlying the pleiotropic effects of this molecule. This membrane remodeling may act in synergy with the other known effects of mycolactone on its intracellular targets, potentiating these effects.