Archaeal lipids: Structural features and supramolecular organization

The Archaea domain, formed exclusively of extremophilic prokaryotic organisms, represents a third evolutive line distinct from the well-known Eubacteria and Eukarya domains. Archaeal lipids are based on ether links and their aliphatic components are isoprenic in nature. Of particular interest are the unusual C40 isoprenoidic bipolar tetraether lipids present in some thermophilic Archaea. These molecules are the structural components of a new model of biological membrane in which a monolayer of bipolar lipids replaces the conventional bilayer of monopolar lipids universally present in the biological membranes. The organization of archaeal lipids between two water environments has been studied using as models black membranes and liposomes. In these structures, characterized by an exceptionally long-term stability, the bipolar lipids are organized to form a monolayer of fully stretched molecules. The behavior of the archaeal lipids at the air-water interface and morphology of the deposited LB films indicate that a U-shaped conformation appears in general to be preferred over an extended conformation in which each bipolar lipid spans the entire monolayer thickness.