Special Issue "Marine Lipopolysaccharides"
A special issue of Marine Drugs (ISSN 1660-3397).
Deadline for manuscript submissions: closed (30 April 2015).
2. Department of Chemical Sciences, University of Napoli Federico II, Complesso Universitario Monte Santangelo, Via Cintia 4, I-80126 Napoli, Italy
Interests: innate immunity; bacterial cell wall; Lipopolysaccharides; peptidoglycan; microbial glycobiology
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Marine bacteria are microorganisms that have adapted, through millions of years, to the survival in environments often characterized by one or more physico-chemical extreme parameters, such as pressure, temperature and salinity. The main interest in the research about marine bacteria is due to their ability to produce several biologically active molecules, such as antibiotics, toxins and antitoxins, antitumor and antimicrobial agents.
Lipopolysaccharides, LPSs, composing about 75% of the outer membrane of Gram negative bacteria and exposed toward the external environment, play an essential role in the adaptation of the organisms to the peculiar external surroundings. The study of LPS primary structure and the (supra)molecular architecture of such molecules is related to the possibility of thriving in marine habitats, shielding the cell from the disrupting action of natural stress factors.
LPSs are build up according to a common structural architecture and are composed of a hydrophilic hetero-polysaccharide (formed by core oligosaccharide and O-specific polysaccharide or O-chain) covalently linked to a lipophilic moiety termed lipid A, which is embedded in the outer leaflet and anchors these macromolecules to the membrane through electrostatic and hydrophobic interactions. LPSs not containing O-chain are termed Rough (R-) LPSs or lipooligosaccharides (LOSs). LOSs may occur in both wild and laboratory strains possessing mutations in the genes encoding the O-specific polysaccharide biosynthesis or transfer. Lipid A possesses a rather conservative structure consisting of α-(1→6)-glucosamine disaccharide backbone phosphorylated at positions 1 and 4’ and acylated with primary 3-hydroxy fatty acids at positions 2 and 3 of both GlcN residues; the hydroxyl groups of the primary fatty acids can be further acylated by secondary acyl moieties. In the core oligosaccharide an inner and outer region are usually distinguished: the inner core, proximal to the lipid A, consists of typical monose residues as Kdo (3-deoxy-D-manno-ocutolonic acid) and heptoses, often carrying negatively charged groups. Kdo is attached to the GlcN II of lipid A backbone and is the first sugar of the core oligosaccharide. The outer core region is more variable and is usually composed by hexoses. The LPS adaptive and dynamic changes managed by Gram-negative bacteria act on the carbohydrate backbone, on the polar heads and the acyl chain composition, and show the primary protective role that the LPSs operate in bacteria.
Another main reason to study LPS structure from marine bacteria is that the LPS lipid A is the primary immuno-stimulator centre of Gram negative bacteria, it triggers the activation of the innate immune system of eukaryotics (both animals and plants) through the interaction with particular proteins called pathogen related receptors, such as the toll like receptors in mammals. The toxicity of the lipid A is depending on its primary structure. The study of lipid A structures from non-toxic Gram-negative bacteria is extremely important in order to identify lipid A analogues which can antagonise the biological activation of competent mammalian host-cells by lipid A. Within this frame, lipopolysaccharides (LPSs), or their portions, from marine bacteria, have often shown low virulence, and represent potential candidates in the development of drugs to prevent septic shock.
The primary and secondary structure of a lipopolysaccharide is attained by a combinatiuon of chemical and biochemical techniques and state-of-art MS spectrometry and NMR spectroscopy.
Prof. Dr. Antonio Molinaro
Manuscript Submission Information
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- lipid A
- marine bacteria
- NMR spectroscopy
- mass spectrometry