4. The basics of lipids and membrane structure

1. Introduction Introduction Lipid molecule : hydrophobic (water-hating), non-polar hydrocarbon chains : hydrophilic (water-loving), polar head groups FIGURE 4.1 A cartoon of four representative lipid aggregate structures.

1. Introduction Why membrane lipids form aggregates FIGURE 4.2 Thylakoid membranes from a chloroplast illustrating the sharp bends (at the arrows) between the flat regions. Why membrane lipids form aggregates When the different structures are formed How the physicochemical properties of the lipids are used by the cell

2.1 lipid classes and their properties

2.1 lipid classes and their properties FIGURE 4.3 Representative structures for each lipid category.

2.1 lipid classes and their properties FIGURE 4.4 A dipalmitoylphospholipid molecule where the chiral carbon on the glycerol moiety is indicated. FIGURE 4.5 Phosphatidylcholine with some of the most common fatty acyl chains.

2.1 lipid classes and their properties Phosphatidylcholine position

2.1 lipid classes and their properties 2.1.1 Phospholipids phosphocholine Glycerophospholipid Sphingophospholipid spingosine Fatty acid FIGURE 4.6 Example of components constituting up a sphingomyelin lipid. phosphatidylinositol

2.2 Membrane lipids form liquid crystalline phases FIGURE 4.8 Structures of some common liquid crystalline phases.

2.2 Membrane lipids form liquid crystalline phases Calorimetric: temperature-composition X-ray scattering(SAXS) spectroscopic 2.2.1 Gibbs phase rule and description of phase behavior (Lamellar liquid crystalline) * F+p=c+2 F+p=c+1 F: degrees of freedom p: coexisting phases c: components 2: temperature, pressure (Gel) dipalmitoylphosphatidylcholine FIGURE 4.7 A partial phase diagram of DPPC and water.

2.2 Membrane lipids form liquid crystalline phases 2.2.1 Gibbs phase rule and description of phase behavior FIGURE 4.9 A partial phase diagram of the system monoglucosyldiacylglycerol (MGlcDAG)/heavy water, where MGlcDAG comes from the bacterium A. laidlawii.

3.1 Lipid packing and spontaneous curvature FIGURE 4.10 As an example of a typical lipid, the figure shows a phospholipid .

3.1 Lipid packing and spontaneous curvature packing parameter FIGURE 4.11 A schematic drawing of the shape of a lipid molecule forming spherical micelles. * P=v/al FIGURE 4.12 Lipid molecules of different shapes and packing parameters. v: volume of the fluid hydrocarbon chains l: length of the hydrophobic chain a: optimal cross-sectional area of the polar head group

3.1 Lipid packing and spontaneous curvature FIGURE 4.13 Left: The definition of the two radii of membrane curvature. Right: illustration of the definition of the sign of the radius of curvature (by conbention).

3.1 Lipid packing and spontaneous curvature Formation of HII phase Curvature energy : Acyl chains must stretch to fill the hydrophobic regions Packing energy Hydrophobic region FIGURE 4.14 As the shape of the lipid molecules (enlarged) get less wedge-shaped, the radius of curvature of the cylinders building up the HII phase increases and the water (blue) uptake increases in the HII cylinders.

3.1 Lipid packing and spontaneous curvature bicontinuous cubic phases sponge (L3) phase FIGURE 4.15 Schematic illustration of the structure of one of the bicontinuous cubic phases. FIGURE 4.16 A schematic picture of a sponge (L3) phase.

3.1 Lipid packing and spontaneous cruvature 3.1.1 Lipid packing and lateral pressure ① ② ③ FIGURE 4.17 Illustration of the lateral pressure, p(z), profile in a lipid bilayer. FIGURE 4.18 High lateral pressure, p(z), can result in a change in the conformation of an integral membrane protein (striped or dashed) as illustrated by the cross-section A(z).

3.1 Lipid packing and spontaneous cruvature 3.1.1 Lipid packing and lateral pressure FIGURE 4.19 The structure of the closed state of the large membrane channel, MscL, in M. tuberculosum outer membrane viewed perpendicularly to the membrane surface. FIGURE 4.20 A schematic picture of the effect on the bilayer curvature (and therefore on the lateral pressure) and a mechanosensitive protein (MscL). Microbiol. Mol. Biol.Rev. 2003

4.1 Regulation of membrane lipid composition Acyl chain structure Polar head group structure Reshuffling of the acyl chains to form new lipid species 4.1.1 Escherichia coli FIGURE 4.21 The bacterium E. coli grows in a “window.”

4.1 Regulation of membrane lipid composition 4.1.2 Acholeplasma laidlawii: 아코이에플라스마 라이들라위이 FIGURE 4.22 Structure of the gluco- and phospholipids in the A. laidlawii membrane: 1. MGlcDAG; 2. MAMGlcDAG; 3. DGlcDAG; 4. MADGlcDAG; 5. GPDGlcDAG; 6. MABGPDGlcDAG.

4.1 Regulation of membrane lipid composition 4.1.2 Acholeplasma laidlawii 아코이에플라스마 라이들라위이 FIGURE 4.23 The bacterium A. laidlawii grows when its lipids are in a lamellar state. FIGURE 4.24 Acyl chain unsaturation as a function of the chain length in the membrane of surviving A. laidlawii bacteria.

4.2 Role of nonlamellar-forming lipids in membrane function 4.2.1 Special membrane structures Nonlamellar-forming lipids  nonbilayer or bilayer structure with a small radius of curvature Nonlamellar structure  fusion ,fission (융합 분열) 4.2.2 Influence on the activity of membrane-associated proteins Efficiency of protein incorporation  lipids forming nonbilayer structures  molecules known to destabilize the bilayer structure

4.3 Membrane fusion Membrane fusion: membrane trafficking, vesicle-mediated transport, sperm-egg fusion, virus-cell fusion FIGURE 4.25 Above. Steps in the fusion of membrane.

Vesicle docking using ER-to-Golgi transport in yeast The vesicle docking is specified by tethering complex restricted to TRAPP location

4.4 Lipid synthesizing enzymes FIGURE 4.26 A cartoon showing how the cell can regulate membrane elastic stress upon binding of CCT (green) to a DOPE (left) in comparison to a DOPC (right) bilayer. Phosphocholine cytidylycerol

4.5 Lipid domains and rafts in membranes fluid mosaic model FIGURE 4.27 A cartoon of the fluid mosaic model of a biological membrane from 1972 according to Singer and Nicolson. FIGURE 4.28 Above: Cholesterol induces lateral phase separation into domains in the membrane containing glycerophospho- and sphingolipids.

4.5 Lipid domains and rafts in membranes FIGURE 4.29 Generic temperature/concentration phase diagram of a system with a saturated phospholipid, cholesterol (CHOL) and water.

4.5 Lipid domains and rafts in membranes Caveolae : lipid raft subtype : caveolin – scaffold protein FIGURE 4.30 Picture of the flask-like invaginations called caveola in the plasma membrane.