Cryo-TEM and NMR studies of a micelle-forming phosphoglucolipid from membranes of Acholeplasma laidlawii A and B

The chemical structure of a phosphoglucolipid from the membrane of the bacterium Acholeplasma laidlawii strain B-PG9 has been determined by high resolution NMR to be 1,2-diacyl-3- O-[glycerophosphoryl-6- O-( α- d-glucopyranosyl-(1→2)- O- α- d-glucopyranosyl)]- sn-glycerol (GPDGlcDAG). It was concluded that this lipid has exactly the same structure as one of the phosphoglucolipids from A. laidlawii strain A-EF22. By cryo transmission electron microscopy (cryo-TEM) and NMR diffusion techniques it was shown that, in highly diluted aqueous solutions, this membrane lipid forms long thread-like micelles in equilibrium with lipid vesicles. The cause of the occurrence of these different aggregates is discussed in terms of the varying molecular shapes of the lipid because of a heterogeneous composition of the acyl chains. A second membrane phosphoglucolipid from the bacterium, namely 1,2-diacyl-3- O-[glycerophosphoryl-6- O-( α- d-glucopyranosyl-(1→2)-monoacylglycerophosphoryl-6- O- α- d-glucopyranosyl)]- sn-glycerol (MABGPDGlcDAG), was found to form only a lamellar liquid crystalline phase coexisting with water.