Core oligosaccharide
Encyclopedia
Core oligosaccharide is a short chain of sugar residues within Gram-negative
lipopolysaccharide (LPS)
. Core-OS are highly diverse among bacterial species and even within strains of species
and commonly contains sugar
s such as heptose
and 3-deoxy-D-mannooctulosonic acid
(also known as KDO, keto-deoxyoctulosonate). The LPS Cores of many bacteria also contain non-carbohydrate components, such as phosphate, amino acids, and ethanolamine substitutents.
Many core structures have been described in the literature, this description is based on the traditional general structure (as found in enteric bacteria and Pseudomonads). See the figure above for an overview of the structure found in E. coli R1.
or ethanolamine
group. From the KDOs, there are attached 2–3 heptose
s (i.e. L-glycero-D-mannoheptulose) that are usually phosphorylated. These KDO and heptoses comprise the "inner core".
The ketosidic bond between KDO and lipid A (α2→6) is especially susceptible to acid cleavage. LPS researchers use a weak acid treatment to separate the lipid and polysaccharide portions of LPS.
An LPS molecule that includes only a lipid A and an inner core (or less. See example) is referred to as "deep-rough LPS".
residues that are attached to the last heptose residue in the inner core. Hexoses often found in the outer core include: D-glucose
, D-mannose
, D-galactose
, etc.. There is usually at least three hexoses bound β1→3, with the O antigen being ligated to the third hexose. Other hexose are often found attached to the outer core, branching from the main oligomer.
LPS that include lipid A and a complete core oligosaccharide (inner and outer) is referred to as "rough LPS."
Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
lipopolysaccharide (LPS)
Lipopolysaccharide
Lipopolysaccharides , also known as lipoglycans, are large molecules consisting of a lipid and a polysaccharide joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria, act as endotoxins and elicit strong immune responses in animals.-Functions:LPS is the major...
. Core-OS are highly diverse among bacterial species and even within strains of species
Structure
The core domain always contains an oligosaccharide component which attaches directly to lipid ALipid A
Lipid A is a lipid component of an endotoxin held responsible for toxicity of Gram-negative bacteria. It is the innermost of the three regions of the lipopolysaccharide molecule, and its hydrophobic nature allows it to anchor the LPS to the outer membrane...
and commonly contains sugar
Sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
s such as heptose
Heptose
A heptose is a monosaccharide with seven carbon atoms.They have either an aldehyde functional group in position 1 or a ketone functional group in position 2 ....
and 3-deoxy-D-mannooctulosonic acid
3-Deoxy-D-manno-oct-2-ulosonic acid
3-Deoxy-D-manno-oct-2-ulosonic acid or KDO is an ulosonic acid of a 2-ketooctose which is used by bacteria in the synthesis of lipopolysaccharides. The D-manno prefix indicates that four chiral centers have the same configuration as D-mannose....
(also known as KDO, keto-deoxyoctulosonate). The LPS Cores of many bacteria also contain non-carbohydrate components, such as phosphate, amino acids, and ethanolamine substitutents.
Many core structures have been described in the literature, this description is based on the traditional general structure (as found in enteric bacteria and Pseudomonads). See the figure above for an overview of the structure found in E. coli R1.
Inner core
The "base" of the inner core is 1–3 KDO residues. The last KDO is often modified with a phosphatePhosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
or ethanolamine
Ethanolamine
Ethanolamine, also called 2-aminoethanol or monoethanolamine , is an organic chemical compound that is both a primary amine and a primary alcohol . Like other amines, monoethanolamine acts as a weak base...
group. From the KDOs, there are attached 2–3 heptose
Heptose
A heptose is a monosaccharide with seven carbon atoms.They have either an aldehyde functional group in position 1 or a ketone functional group in position 2 ....
s (i.e. L-glycero-D-mannoheptulose) that are usually phosphorylated. These KDO and heptoses comprise the "inner core".
The ketosidic bond between KDO and lipid A (α2→6) is especially susceptible to acid cleavage. LPS researchers use a weak acid treatment to separate the lipid and polysaccharide portions of LPS.
An LPS molecule that includes only a lipid A and an inner core (or less. See example) is referred to as "deep-rough LPS".
Outer core
The outer core is made of hexoseHexose
In organic chemistry, a hexose is a monosaccharide with six carbon atoms, having the chemical formula C6H12O6. Hexoses are classified by functional group, with aldohexoses having an aldehyde at position 1, and ketohexoses having a ketone at position 2....
residues that are attached to the last heptose residue in the inner core. Hexoses often found in the outer core include: D-glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
, D-mannose
Mannose
Mannose is a sugar monomer of the aldohexose series of carbohydrates. Mannose is a C-2 epimer of glucose. It is not part of human metabolism, but is a component of microbial cell walls, and is therefore a target of the immune system and also of antibiotics....
, D-galactose
Galactose
Galactose , sometimes abbreviated Gal, is a type of sugar that is less sweet than glucose. It is a C-4 epimer of glucose....
, etc.. There is usually at least three hexoses bound β1→3, with the O antigen being ligated to the third hexose. Other hexose are often found attached to the outer core, branching from the main oligomer.
LPS that include lipid A and a complete core oligosaccharide (inner and outer) is referred to as "rough LPS."