A heptose is a monosaccharide with seven carbon atoms.
They have either an aldehyde functional group in position 1 ( aldoheptoses) or a ketone functional group in position 2, 3 or 4 ( ketoheptoses). Ketoheptoses have 4 chiral centers, whereas aldoheptoses have 5.
Examples
There are few examples of seven-carbon sugars in nature, among which are:
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sedoheptulose or D- altro-heptulose (a ketose), an intermediate in the Calvin cycle and in lipid A biosynthesis
-
mannoheptulose (a ketose), found in
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L- glycero-D- manno-heptose (an aldose), a late intermediate in lipid A biosynthesis.
Structural role
The production of heptose is conserved across gram-negative bacteria. In the form of L-glycero-D-mannose-heptose, heptose is a key component in the secondary membrane of gram-negative bacteria. Gram-negative bacteria, in addition to having a
cell wall, are also encapsulated by a membrane composed of lipopolysaccharides.
These lipopolysaccharides comprise an
endotoxin that acts as an immune system
agonist and elicits strong responses. This toxin, known as
lipid A, consists of a core of one to three heptose molecules.
The 7-carbon heptose molecules are essential for stability in the lipopolysaccharide membrane, forming an interconnected network utilizing divalent cations.
Role in cell signaling
Heptose, in the form of heptose 1-7-bisphosphate, has been found to be one of the components responsible for the
Pathogen nature of gram negative bacteria. In the bacterium biosynthesis pathway, heptose is
Phosphorylation to heptose 1-7-bisphosphate. In addition, like other sugars, heptose may exist in either the
Anomer or the
Anomer. Before synthetic production of heptose-bisphosphate (HBP) for studies, cytosolic HBP was thought to influence NF-kB, a transcription factor in mammalian cells.
Along with producing the first synthetic version of HBP, it was shown that the beta form of the heptose acts as a pathogen-associated molecular pattern (PAMP) and activates the NF-kB signaling pathway.
A PAMP is a specific structure, component, or molecule that triggers the immune response after recognition by pattern recognition receptors on mammalian cells.
