Influence of Ether Bonds and Branched Lipid Tails on Stability of Membranes to Pore Formation

Abstract

Archaeal lipid membranes have a number of unique structural features that distinguish them from those of bacteria and eukaryotes allowing archaea to survive in harsh environments, such as high temperature, increased acidity and pressure. To date the data on the impact of certain peculiarities of archaeal lipids on its membrane properties are fragmentary and insufficient for the understanding of their functioning. In general, archaea contain diether and tetraether lipids with chemically stable ether bond. Archaeal lipid tails are fully saturated (with rare exceptions) isoprenoid chains and sometimes contain cyclopropane and/or cyclohexane rings. Such structure of the hydrophobic part of the molecule not only helps the archaea to live at high temperatures, but also protects their membranes from harmful influence of various phospholipases, secreted by other organisms, and from oxidative stress. However, the role of the branched chain structure in the permeability of archaeal membranes to various ions, gases and water is still an open question. Pores, being conducting defects in a membrane, are the one of the most general causes of loss of membrane barrier function leading to cell death. So structural peculiarities of archaeal lipid should have some influence on membrane resistance to pore formation. We have studied process of pore formation in bilayer lipid membranes formed by ether and ester branched and unbranched lipids using electrical breakdown technique and molecular dynamics simulations. We have shown that branched lipid tails have a great influence on probability of pore formation and dynamics of its growth. A theoretical model connecting pore edge line tension and dynamics of pore widening was proposed.