75px, Lipopolysaccharide. The core includes both the inner and outer core. Core oligosaccharide (or Core-OS) is a short chain of sugar residues within

Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

lipopolysaccharide (LPS). Core-OS are highly diverse among bacterial species and even within strains of species

Structure

600px, Core-OS Structure and Metabolic Pathways: oligosaccharide from '' Escherichia coli'' R1. Inner core is represented in green and outer core is represented in blue. The core domain always contains an oligosaccharide component which attaches directly to

lipid A Lipid A is a lipid component of an endotoxin held responsible for the toxicity of gram-negative bacteria. It is the innermost of the three regions of the lipopolysaccharide (LPS), also called endotoxin molecule, and its hydrophobic nature allows ...

and commonly contains

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecul ...

s such as heptose and 3-deoxy-D-mannooctulosonic acid (also known as KDO or keto-deoxyoctulosonate). The LPS Cores of many bacteria also contain non-carbohydrate components, such as

phosphate Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

s, and

ethanolamine Ethanolamine (2-aminoethanol, monoethanolamine, ETA, or MEA) is a naturally occurring organic chemical compound with the formula or . The molecule is bifunctional, containing both a primary amine and a primary alcohol. Ethanolamine is a colorl ...

substituents. Many core structures have been described in the literature, this description is based on the ''traditional'' general structure (as found in enteric bacteria and ''

Pseudomonas ''Pseudomonas'' is a genus of Gram-negative bacteria belonging to the family Pseudomonadaceae in the class Gammaproteobacteria. The 348 members of the genus demonstrate a great deal of metabolic diversity and consequently are able to colonize a ...

''). See the figure above for an overview of the structure found in ''

E. coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escherichia'' that is commonly foun ...

'' R1.

Inner core

The "base" of the inner core is 1–3 KDO residues. The last KDO is often modified with a

group. From the KDOs, there are attached 2–3 heptoses (i.e. L-glycero-D-''manno''heptulose) 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

hexose In chemistry, a hexose is a monosaccharide (simple sugar) with six carbon atoms. The chemical formula for all hexoses is , and their molecular weight is 180.156 g/mol. Hexoses exist in two forms, open-chain or cyclic, that easily convert into ...

residues that are attached to the last heptose residue in the inner core. Hexoses often found in the outer core include: D-

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

, D-

mannose Mannose is a sugar with the formula , which sometimes is abbreviated Man. It is one of the monomers of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylatio ...

, D-

galactose Galactose (, ''wikt:galacto-, galacto-'' + ''wikt:-ose#Suffix 2, -ose'', ), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweetness, sweet as glucose, and about 65% as sweet as sucrose. It is an aldohexose and a C-4 epime ...

, ''etc.''. There are 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."

Biosynthesis

The enzymes involved in core oligosaccharide synthesis are conserved among ''

Escherichia coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...

'' and ''

Salmonella ''Salmonella'' is a genus of bacillus (shape), rod-shaped, (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two known species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' ...

''. ''

Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common Bacterial capsule, encapsulated, Gram-negative bacteria, Gram-negative, Aerobic organism, aerobic–facultative anaerobe, facultatively anaerobic, Bacillus (shape), rod-shaped bacteria, bacterium that can c ...

'' has some unique enzymes.

Function

The mechanism whereby the core oligosaccharide of lipopolysaccharide affect the membrane behavior is not well understood.

References