Mesomorphic phases and phase transitions in membranes, biomechanical aspects

R. Koynova, B. Tenchov

Abstract: Lipids represent a large, chemically diverse class of biological molecules with varied biological roles. Their major function is to serve as building blocks of the biological membranes. According to the fluid-mosaic model, the biomembranes are liquid-crystalline lipid bilayers with embedded proteins. However, in addition to bilayer-forming lipids, the lipids in the biomembranes include a large fraction of species that, in isolation, adopt curved nonlamellar (hexagonal, cubic, etc.) structures rather than the lamellar state. Consequently, except for the lamellar liquid crystalline phase (the ‘membrane’ phase), the membrane lipids are also able to form a large variety of other phases with different geometry and molecular organization. These phases transform into each other via different types of phase transitions. The abundant diversity of the membrane lipids and their ability to self-assemble into various crystalline, gel and liquid-crystalline phases represent their most intriguing features involved in various cellular processes. The physiological importance of lipid diversity and mesomorphism stems from the possibility to finely tune the biomembrane properties and modulate the lipid phase state in broad limits by altering the lipid chemical structure and composition. The mutual transformations between the lipid liquid crystalline (mesomorphic) phases, their biomechanical aspects such as the roles of curvature elasticity and packing energetics in controlling the stability of these phases, as well as their physiological implications, are the subject of the present review.

Series on Biomechanics, Vol.31, No.2 (2017), 3-19

Keywords: biomechanics; Cubic phase; curvature elasticity; hexagonal phase; membrane lipid; phase transition

Date published: 2017-10-27