Which of the following lipid modifications increases curvature in membranes?
Membrane bending energy is governed by molecular geometry quantified as shape parameter defined as volume over area times length. Phosphatidylethanolamine possesses small ethanolamine headgroup about zero point two eight square nanometers versus larger hydrocarbon volume due to two acyl chains, creating conical shape with parameter greater than one favoring negative spontaneous curvature typical of inner leaflet concave tubules and fusion stalk intermediates. Enrichment of PE in cytoplasmic leaflet at SNARE assembly sites reduces hydration repulsion and elastic cost of merging outer leaflets first forming hemifusion diaphragm. Influenza hemagglutinin fusion peptide inserts and recruits PE; reconstituted PE containing liposomes fuse rapidly upon calcium addition while pure phosphatidylcholine liposomes are fusogen resistant. Enzymes phosphatidylserine decarboxylase PSD in mitochondria inner membrane generate curvature for cristae formation. Flippases maintain PE asymmetry. Lysophospholipids opposite shape induce positive curvature inhibiting stalk formation. Cholesterol buffers rigidity but modest curvature effect. Appreciating cone versus cylinder concept connects lipid metabolism to exocytosis cytokinesis and viral entry mechanisms thoroughly asked in examinations.
Ref: Chernomordik & Kozlov, Nature Structural Biology 2003, PE and membrane curvature in fusion.