Question

Utilize lipid packing models to design a hairpin turn in a membrane--- use the shapes of a cylinder, cone and inverted cone to stimulate the way different phospholipids occupy space

Answer 1

To describe the model I have listed three groups of lipids, based on this group composition I will build hairpin turn in a membrane

Group1: Cylinder shaped lipids: phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylglycerol (PG), phosphatidylinositol (PI), phosphatidic acid (PA), cardiolipin (CL), sphingomyelins (SM)

Group2: Cone shaped lipids & their conditions: phosphatidylethanolamine (PE unsaturated), phosphatidic acid (PA in the presence of Ca ions and pH< 3), phosphatidylserine (PS pH< 3), cardiolipin (CL in the presence of Ca ions)

Group3: Inverted Cone shaped lipids: Lysophospholipid

Normal lipid bilayer without any bends will be exclusively made of ‘Group1’ lipids. To make an hairpin membrane we need at least three tight bends, in that two juxtaposed bends should be less bent or L shaped turn in the plasma membrane and one tight bend perpendicular to L shaped bends gives a hairpin like turn in a membrane.

Here we will consider lipid bilayer of the plasma membrane. L shaped bends, outer leaflet should be made of ‘group2’ lipids and inner leaflet should be made of ‘group3’ lipids, as L shaped bend is less tight less number of group2 and group 3 lipids are required.

Tight bend perpendicular to L shaped bends outer leaflet should be made of ‘group3’ lipids and inner leaflet should be made of ‘group2’ lipids. To make tight bend more number of group3 and group 2 lipids are required.