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1. (Article ID: 4175)
 
Demel R, Lindblom G, Rilfors L
Packing of a triacylglucolipid from the membrane of Acholeplasma laidlawii strain A at the air/water interface
Biochimica et Biophysica Acta 1190 (1994) 416-420
 

Pressure-area curves were generated at 22 degrees C and 40 degrees C for three glucolipids isolated from Acholeplasma laidlawii strain A-EF22. The glucolipids are 1,2-diacyl-3-O-(α-D-glucopyranosyl)-sn-glycerol (MGlcDAG), 1,2-diacyl-3-O-[α-D-glucopyranosyl-(1→2)-O-α-D-glucopyranosyl]-sn-glycerol (DGlcDAG), and 1,2-diacyl-3-O-[3-O-acyl-(α-D-glucopyranosyl)]-sn-glycerol (MAMGlc-DAG). The curves for MGlcDAG and DGlcDAG are characteristic for monolayers in a liquid phase at both temperatures. MGlcDAG has a smaller molecular area at all surface pressures compared to DGlcDAG. At 22 degrees C MAMGlcDAG shows a phase transition at 13 mN/m. However, at 40 degrees C the pressure-area curve for this lipid is characteristic for a monolayer in a liquid state. Mixed MAMGlcDAG-DGlcDAG and MGlcDAG-DGlcDAG monolayers showed no significant deviation from the additivity rule at 40 degrees C. The area per acyl chain is nearly the same for MAMGlcDAG and MGlcDAG. Our study supports our previous results that aqueous dispersions of these lipids form non-lamellar, reversed aggregates.

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2. (Article ID: 4186)
 
Hauksson JB, Lindblom G, Rilfors L
Structures of glucolipids from the membrane of Acholeplasma laidlawii strain A-EF22. I. Glycerophosphoryldiglucosyldiacylglycerol and monoacylbisglycerophosphoryldiglucosyldiacylglycerol
Biochimica et Biophysica Acta 1214 (1994) 124-130
 

The structures of two phosphoglucolipids from the membrane of Acholeplasma laidlawii, strain A-EF22 were determined by high resolution 13C-, 31P- and 1H-NMR. The lipids in question are 1,2-diacyl-3-O-[glycerophosphoryl-6-O-(α-D-glucopyranosyl-(1→2)-O-α-D-glucopyranosyl)]-sn-glycerol (1) and 1,2-diacyl-3-O-[glycerophosphoryl-6-O-(α-D-glucopyranosyl-(1→2)-monoacyl-glycerophosphoryl-6-O-α-D-glucopyranosyl)]-sn-glycerol (2). Both lipids are thus derivatives of diglucosyldiacylglycerol. Previous reports on these lipids, based on insufficient chemical analyses, showed contradictory structures. A phosphoglycolipid having the structure of 2 has not been described previously.

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3. (Article ID: 4204)
 
Hauksson JB, Lindblom G, Rilfors L
Structures of glucolipids from the membrane of Acholeplasma laidlawii strain A-EF22. II. Monoacylmonoglucosyldiacylglycerol
Biochimica et Biophysica Acta 1215 (1994) 341-345
 

The structure of one glucolipid from the membrane of Acholeplasma laidlawii, strain A-EF22, was determined. This glucolipid is synthesized only when a large fraction of saturated, straight-chain fatty acids are incorporated into the membrane lipids of strain A-EF22. The lipid was studied by 1H- and 13C-NMR spectroscopy. The structure of the lipid is 1,2-diacyl-3-O-[6-O-acyl-(α-D-glucopyranosyl)]-sn-glycerol. The result for this lipid shows that a previously published structure, based on incomplete chemical analyses, was incorrect. The phase equilibria for 1,2-diacyl-3-O-[6-O-acyl-(α-D-glucopyranosyl)]- sn-glycerol and the two dominating lipids in A. laidlawii, monoglucosyldiacylglycerol and diglucosyldiacylglycerol, are discussed and related to the chemical structure of the lipids.

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4. (Article ID: 4211)
 
Karlsson OP, Dahlqvist A, Wieslander A
Activation of the membrane glucolipid synthesis in Acholeplasma laidlawii by phosphatidylglycerol and other anionic lipids
Journal of Biological Chemistry 269 (1994) 23484-23490
 

In membrane lipids of the prokaryote Acholeplasma laidlawii similar phase equilibria and a nearly constant spontaneous curvature are maintained by an extensive metabolic regulation of especially the major polar lipids monoglucosyldiacylglycerol (MGlcDAG) and diglucosyldiacylglycerol (DGlcDAG), forming nonlamellar and lamellar phases, respectively. A constant surface charge density is maintained by the anionic phospholipid fraction. These lipids are synthesized from phosphatidic acid in two competing pathways. The in vitro synthesis of MGlcDAG and DGlcDAG were totally lost upon delipidation of the membrane proteins by detergent solubilization or solvent extraction of lyophilized cells. Activities were restored by critical concentrations of anionic lipids, but not by bilayer or nonbilayer zwitterionic phospholipids or glucolipids. Phosphatidylglycerol (PG), and to a lesser extent certain other anionic lipids, could activate the synthesis of MGlcDAG in lipid bilayers, whereas the synthesis of DGlcDAG was similarly dependent upon PG only. Two endogenous phosphoglucolipids with no activating potency could partially replace the PG activator for the MGlcDAG synthesis but less so for DGlcDAG formation. A change of inert matrix from phosphatidylcholine to DGlcDAG lowered the apparent cooperativity, but enhanced the efficiency, of activation by PG for both glucolipid synthesizing enzymes, most strongly the synthesis of DGlcDAG. These results indicate that the enzymatic formation of MGlcDAG is regulated by the lipid surface charge density, whereas the consecutive step to DGlcDAG is more dependent upon the specific properties of PG. The modulating effect of the surrounding matrix on the activator efficiencies and cooperativity may constitute part of the bilayer-nonbilayer lipid regulation mechanism.

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