Nucleotide sugar
From Wikipedia, the free encyclopedia
Nucleotide sugars are the activated forms of monosaccharides. Nucleotide sugars act as glycosyl donors in glycosylation reactions. Those reactions are catalyzed by a group of enzymes called glycosyltransferases.
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[edit] History
The anabolism of oligosaccharides - and, hence, the role of nucleotide sugars - was not clear until 1950s when Leloir and his coworkers found that the key enzymes in this process are the glycosyltranserases. These enzymes transfer a glycosyl group from a sugar nucleotide to an acceptor.[1]
[edit] Biological Importance
To act as glycosyl donors, those monosaccharides should exist in a highly energetic form. This occurs as a result of a reaction between nucleoside triphosphate (NTP) and glycosyl monophosphate (phosphate at anomeric carbon).
[edit] Types
There are nine sugar nucleotides in complex animals which act as glycosyl donors and they can be classified depending on the type of the nucleoside forming them[2] :
- Uridine Diphosphate: UDP-Glc, UDP-Gal, UDP-GlcNAc, UDP-GlcUA, UDP-Xyl
- Guanine Diphosphate: GDP-Man, GDP-Fuc.
- Cytosine Monophosphate: CMP-Neu5Ac, it is the only nucleotide sugar in the form of nucleotide monophosphate.
In plants and bacteria many other sugars are used and various donors are utilized for them. Specifically, CDP-glucose and TDP-glucose are found in nature and give rise to various other forms of CDP and TDP-sugar donor nucleotides.[3][4]
[edit] Structures
listed below are the structures of some nucleotide sugars (example from each type).
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[edit] Relationship between glycosylation pathways and different diseases
Normal metabolism of nucleotide sugars is very important. Any malfunction in any contributing enzyme will lead to a certain disease [5] for example:
- Inclusion body myopathy: is a congenital disease resulted from altered function of UDP-GlcNAc epimerase .
- Macular corneal dystrophy: is a congenital disease resulted from malfunction of GlcNAc-6-sulfotransferase.
- Congenital disorder in α-1,3 mannosyl transferase will result in a variety of clinical symptoms, e.g. hypotonia, psychomotor retardation, liver fibrosis and various feeding problems.
[edit] See also
[edit] References
- ^ Derek Horton (2008). "The Development of Carbohydrate Chemistry and Biology". Carbohydrate Chemistry, Biology and Medical Applications: 1–28. doi:.
- ^ Cold Spring Harbor Laboratory Press Essentials of Glycobiology, Second Edition
- ^ Samuel G, Reeves P (2003). "Biosynthesis of O-antigens: genes and pathways involved in nucleotide sugar precursor synthesis and O-antigen assembly". Carbohydr. Res. 338 (23): 2503–19. doi:. PMID 14670712.
- ^ Xue M. He and Hung-wen Liu (2002). "Formation of unusual sugars: Mechanistic studies and biosynthetic applications". Annu Rev Biochem 71: 701-754.
- ^ [Encyclopedia of Biological Chemistry, Volume 2. 2004, Elsevier Inc. Hudson H. Freeze 302-307.
[edit] External links
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