Efficient modulation of glucolipid enzyme activities in membranes of Acholeplasma laidlawii by the type of lipids in the bilayer matrix.
It is generally anticipated, but so far not fully shown, that the physical properties of membrane lipid bilayers are governed by the concerted actions of the lipid-synthesizing enzymes. In the membrane of Acholeplasma laidlawii a constant surface charge density, similar phase equilibria, and a nearly constant spontaneous curvature are maintained for the polar lipids. Important for these properties are monoglucosyldiacylglycerol (MGlcDAG) and diglucosyldiacylglycerol (DGlcDAG), forming mainly reversed nonlamellar and lamellar phases, respectively. The syntheses of these lipids (from 1,2-DAG and MGlcDAG) by two consecutively acting, membrane-bound glucosyltransferases have been analyzed in synthetic lipid bilayers of selected physical properties. Both enzymes demanded the presence of activator lipids; for MGlcDAG synthesis a critical fraction of anionic lipids was important, whereas for the DGlcDAG synthesis substantial amounts of a liquid-crystalline phosphatidylglycerol (PG) with a certain chain length were essential. The rates of the syntheses for the two glucolipids increased with decreasing chain length of the DAG and MGlcDAG substrates. The enzymatic formation of DGlcDAG (bilayer-forming) was influenced in a dose-dependent manner by the nonbilayer (curvature) propensities of several amphiphilic and hydrophobic lipids in two different bilayer matrixes. However, the preceding synthesis of the nonlamellar MGlcDAG was only affected to a minor extent by such additives. The mechanism for modulation involved an enhancement of the activating potencies of PG in a cooperative fashion at physiological concentrations for PG.(ABSTRACT TRUNCATED AT 250 WORDS)
Dahlqvist
A
A
Department of Biochemistry, Umeå University, Sweden.
Nordström
S
S
Karlsson
O P
OP
Mannock
D A
DA
McElhaney
R N
RN
Wieslander
A
A
D000128:Acholeplasma laidlawii / Q000201:enzymology*; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002462:Cell Membrane / Q000201:enzymology; D004075:Diglycerides / Q000378:metabolism*; D006017:Glycolipids / Q000096:biosynthesis* / Q000737:chemistry; D007700:Kinetics; D008051:Lipid Bilayers; D008563:Membrane Lipids / Q000378:metabolism*; D008969:Molecular Sequence Data; D010715:Phosphatidylglycerols / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D004075:Diglycerides; D006017:Glycolipids; D008051:Lipid Bilayers; D008563:Membrane Lipids; D010715:Phosphatidylglycerols