Lipid molecular shapes and membrane architecture.
A simple biomembrane like erythrocyte contains well over hundred lipid species with diverse molecular shapes differing in the number of acyl chains, chain length, unsaturation and head group composition. A delicate balance between these molecular shapes is necessary in order to have a functional membrane. It is well established that the activities of a number of membrane-bound enzymes and other properties such as aggregation, spontaneous vesiculation, pathophysiological properties and lipid-protein interactions of lipids depend on the acyl chain length, unsaturation and head group composition. In fact, the molecular shape of a phospholipid molecule, as modulated by changes in chain length, unsaturation and head group composition, is probably what is affecting the above mentioned properties. The molecular shape of a lipid depends on a dimensionless packing parameter, S, the value of which influences the size and shape of aggregate formed upon hydration. In fact, the additivity of S values of lipid mixtures explains a number of experimental observations. The molecular shape concept, although very simple, explains many membrane phenomena like complementarity of molecular shapes of non-bilayer lipids to form stable bilayers. Membrane permeability is controlled to a large extent by lipid packing which depends upon molecular shapes. In fact, membranes maintain their lamellar structure by delicately balancing the composition of bilayer-forming and non-bilayer-forming lipids indicating that complementarity of molecular shapes is essential to maintain the permeability barrier. Based on this, the complementary molecular shape model of cell membrane is proposed.
Kumar
V V
VV
Surface Chemistry Section, Hindustan Lever Research Centre, Chakala, Bombay, India.
D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure*; D004910:Erythrocyte Membrane / Q000648:ultrastructure; D006801:Humans; D008051:Lipid Bilayers; D008563:Membrane Lipids / Q000737:chemistry*; D008961:Models, Structural; D008968:Molecular Conformation; D010713:Phosphatidylcholines / Q000737:chemistry
D008051:Lipid Bilayers; D008563:Membrane Lipids; D010713:Phosphatidylcholines