If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Carbohydrates Biosynthesis|
Some taxa known to possess this pathway include : Escherichia coli K-12 substr. MG1655
Expected Taxonomic Range: Proteobacteria
Colanic acid, also known as the M antigen, is an extracellular polysaccharide found in Enterobacteriaceae. It is a polyanionic heteropolysaccharide containing a repeat unit with D-glucose, L-fucose, D-galactose, and D-glucuronate sugars that are nonstoichiometrically decorated with O-acetyl and pyruvate side chains [Grant69, Garegg71]. The sugars need to be activated in the form of nucleotide sugars (UDP-α-D-glucose, GDP-β-L-fucose, UDP-α-D-galactose and UDP-α-D-glucuronate, respectively) prior to their assembly [Stevenson96, Stout96].
The colanic acid polysaccharide repeat is assembled on the membrane lipid all-trans-dodecaprenyl diphosphate by a series of glycosyl transferases on the cytoplasmic face of the inner membrane, after which the single repeat is flipped to the periplasmic side and polymerized by the Wzy-dependent pathway (reviewed in [Raetz02] and [Whitfield06]). Subsequently, the polymer is believed to be cleaved from the all-trans-dodecaprenyl diphosphate anchor, transported across the periplasm, and excreted into the extracellular space, although this process is not well understood.
Colanic acid biosynthesis has been linked to a cluster of 19 genes, which were named wca [Stevenson96, Stout96]. This gene cluster is tightly regulated by a complex signal transduction cascade governed by the rcs (regulator of capsule synthesis) phosphorelay system [Gottesman85, Majdalani05].
Subpathways: GDP-L-fucose biosynthesis I (from GDP-D-mannose) , GDP-mannose biosynthesis , UDP-glucose biosynthesis , UDP-D-galactose biosynthesis , UDP-α-D-glucuronate biosynthesis (from UDP-glucose)
Unification Links: EcoCyc:COLANSYN-PWY
Created 02-Dec-1997 by Pellegrini-Toole A , Marine Biological Laboratory
Revised 29-May-2008 by Caspi R , SRI International
Revised 13-Jun-2008 by Keseler I , SRI International
Revised 15-Aug-2013 by Caspi R , SRI International
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Bauer92: Bauer AJ, Rayment I, Frey PA, Holden HM (1992). "The molecular structure of UDP-galactose 4-epimerase from Escherichia coli determined at 2.5 A resolution." Proteins 12(4);372-81. PMID: 1579570
Baveja86: Baveja UK, Jyoti AS, Kaur M, Agarwal DS, Anand BS, Nanda R (1986). "Isoenzyme studies of Giardia lamblia isolated from symptomatic cases." Aust J Exp Biol Med Sci 64 ( Pt 2);119-26. PMID: 2943257
Berger01a: Berger E, Arabshahi A, Wei Y, Schilling JF, Frey PA (2001). "Acid-base catalysis by UDP-galactose 4-epimerase: correlations of kinetically measured acid dissociation constants with thermodynamic values for tyrosine 149." Biochemistry 40(22);6699-705. PMID: 11380265
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