heptose

There are few examples of seven-carbon sugars in nature, among which are:

• sedoheptulose or D-altro-heptulose (a ketose), an intermediate in the Calvin cycle and in lipid A biosynthesis{{Cite journal | doi = 10.1021/ja01104a532| title = Transaldolase: The Formation of Fructose-6-Phosphate from Sedoheptulose-7-Phosphate| journal = Journal of the American Chemical Society| volume = 75| issue = 8| pages = 2021| year = 1953| last1 = Horecker| first1 = B. L| last2 = Smyrniotis| first2 = P. Z| bibcode = 1953JAChS..75.2021H}}{{Cite journal| doi = 10.1016/j.tibs.2014.06.005 | pmid = 25037503 | title = The pentose phosphate pathway and cancer | journal = Trends in Biochemical Sciences | volume = 39 | issue = 8 | pages = 347–354 | year = 2014 | last1 = Patra | first1 = Krushna C | last2 = Hay | first2 = Nissim | pmc=4329227}}
• mannoheptulose (a ketose), found in avocadoes{{cite journal |last1=Liu |first1=Xuan |last2=Sievert |first2=James |last3=Arpaia |first3=Mary Lu |last4=Madore |first4=Monica A. |title=Postulated Physiological Roles of the Seven-carbon Sugars, Mannoheptulose, and Perseitol in Avocado |journal=Journal of the American Society for Horticultural Science |date=2002-01-01 |volume=127 |issue=1 |pages=108–114 |url=http://journal.ashspublications.org/content/127/1/108.abstract |access-date=2018-06-26 |language=en |doi=10.21273/JASHS.127.1.108 |doi-access=free |url-access=subscription }}
• L-glycero-D-manno-heptose (an aldose), a late intermediate in lipid A biosynthesis.{{Cite journal |last1=Taylor |first1=Patricia L. |last2=Blakely |first2=Kim M. |last3=de Leon |first3=Gladys P. |last4=Walker |first4=John R. |last5=McArthur |first5=Fiona |last6=Evdokimova |first6=Elena |last7=Zhang |first7=Kun |last8=Valvano |first8=Miguel A. |last9=Wright |first9=Gerard D. |last10=Junop |first10=Murray S. |date=1 February 2008 |title=Structure and Function of Sedoheptulose-7-phosphate Isomerase, a Critical Enzyme for Lipopolysaccharide Biosynthesis and a Target for Antibiotic Adjuvants |journal=Journal of Biological Chemistry |language=en |volume=283 |issue=5 |pages=2835–2845 |doi=10.1074/jbc.M706163200|doi-access=free |pmid=18056714 }}

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.{{Cite journal |last1=Gaudet |first1=Ryan G. |last2=Gray-Owen |first2=Scott D. |date=2016-09-22 |title=Heptose Sounds the Alarm: Innate Sensing of a Bacterial Sugar Stimulates Immunity |journal=PLOS Pathogens |language=en |volume=12 |issue=9 |pages=e1005807 |doi=10.1371/journal.ppat.1005807 |doi-access=free |issn=1553-7374 |pmc=5033458 |pmid=27658039}} 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.

Heptose, in the form of heptose 1-7-bisphosphate, has been found to be one of the components responsible for the pathogenic nature of gram negative bacteria. In the bacterium biosynthesis pathway, heptose is phosphorylated to heptose 1-7-bisphosphate. In addition, like other sugars, heptose may exist in either the alpha anomer or the beta anomer. Before synthetic production of heptose-bisphosphate (HBP) for studies, cytosolic HBP was thought to influence NF-kB, a transcription factor in mammalian cells.{{Cite journal |last1=Inuki |first1=Shinsuke |last2=Aiba |first2=Toshihiko |last3=Kawakami |first3=Shota |last4=Akiyama |first4=Taishin |last5=Inoue |first5=Jun-ichiro |last6=Fujimoto |first6=Yukari |date=2017-06-16 |title=Chemical Synthesis of d - glycero - d - manno -Heptose 1,7-Bisphosphate and Evaluation of Its Ability to Modulate NF-κB Activation |url=https://pubs.acs.org/doi/10.1021/acs.orglett.7b01158 |journal=Organic Letters |language=en |volume=19 |issue=12 |pages=3079–3082 |doi=10.1021/acs.orglett.7b01158 |pmid=28541700 |issn=1523-7060|url-access=subscription }} 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.

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{{Carbohydrates}}