STRUCTURAL CHARACTERIZATION OF THE LIPOPOLYSACCHAR1DE FROM A NOVEL HALOALKALOPHILIC BACTERIUM, SALINIVIBRIO SHARMENSIS BAG~T.

摘要

Organisms able to survive in high salt environments are called halophiles. In these hard life conditions the halophiles undergo strong osmotic stress that is overcome by accumulating osmolytes or by maintaining cytoplasmic salt concentration (KCl) close to that of the surrounding medium. As a consequence, proteins from halophiles present negative charged amino acid residues on their surface and membrane phospholipids become more anionic. On the outer leaflet of the external membrane Gram-negative bacteria display lipopolysaccharides (LPS), amphiphilic macromolecules anchored with their lipid part in the phospholipids bilayer. LPSs are constituted by three different regions covalently linked. The lipid A is the glycolipid portion that is connected to the oligosaccharidic region (core), which in turn is substituted by a polysaccharidic region (O-chain). When the O-chain is absent the molecule is named lipooligosaccharide (LOS). Both the oligo- and polysaccharidic region are directed towards the outside of the cell. This location allows the involvement of the LPSs structures into the environmental adaptation mechanisms, as the other components of the cellular membrane, although in this context the role of LPSs is far to be clear. Only the structural characterization of these molecules can help to get deeper in the knowledge of the survival mechanisms of halophiles.