Structure and functional properties of diacylglycerols in membranes.

摘要: 1. 1,2-Diacyl-sn-glycerols (DAG) are minor components of cell membranes (about 1 mole% the lipids) and yet they potent regulators both physical properties lipid bilayer catalytic behaviour several membrane-related enzymes. 2. In pure state DAG's present a considerable polymorphism, with crystalline phases in addition to neat fluid phase. The most stable phase is so-called beta' phase, monoclinic form orthorhombic perpendicular subcell chain packing, which acyl chains lie parallel each other hairpinlike configuration about sn-1 sn-2 glycerol carbon atoms. molecules organized bilayer, backbone roughly plane tilted at approximately 60 degrees respect that plane. Acyl unsaturation, particularly single cis impairs packing mixed-chain DAG's, this results an increased number metastable phases. 3. mix phospholipids bilayers when their melting temperature below or close enough system. When incorporated phospholipid bilayers, conformation DAG such nearly extending from Cl into hydrophobic matrix first surface, then making 90 bend position carbonyl become chain. located two CH2 units deeper than adjacent phospholipids. nonideally phospholipids, giving rise in-plane separations DAG-rich -poor domains, even state. also increase separation between headgroups, decrease hydration surface. Also, because transversal section headgroup small compared chains, favours (negative) curvature monolayers, DAG-phospholipid mixtures tend convert inverted nonlamellar hexagonal cubic 4. A membrane enzyme activities modulated (activated) by DAG, notably protein kinase C, phospholipases enzymes metabolism. Protein C activation (and perhaps as well) occurs combined result DAG-induced modifications include: changes conformation, interspacing hydration, propensity phases, lateral domains. Among DAG-activated enzymes, show peculiarity yielding activator reaction product, allows self-induced transition low- high-activity status. 5. induce enhance fusion ways, mainly through partial dehydration monolayer separation. DAG-increased rates have been demonstrated instances cation-induced model membranes, well Ca(2+)-induced chromaffin granules plasma vesicles. Also phospholipase has shown vesicle aggregation generation bilayers. rather general property it promotes vesicular interparticle aggregation. 6. living cell, often generated degradation response extracellular agonist binding specific receptor said act intracellular second messenger. (ABSTRACT TRUNCATED)