This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Carbohydrates Biosynthesis → Sugars Biosynthesis → Sugar Nucleotides Biosynthesis → CDP-sugar Biosynthesis|
|Biosynthesis → Cell Structures Biosynthesis → Lipopolysaccharide Biosynthesis → O-Antigen Biosynthesis|
Some taxa known to possess this pathway include : Yersinia pseudotuberculosis
Expected Taxonomic Range: Enterobacteriales
A limited number of species of Gram-negative bacteria, all in the family Enterobacteriaceae, utilize unusual sugars, derivatives of 3,6-dideoxyhexose, as an O-antigen of their lipopolysaccharides. These sugars are the dominant antigenic determinants in the membranes of these organisms.
Out of the eight possible stereoisomers of 3,6-dideoxyhexoses, only five have been identified in nature. These are D-abequose, L-ascarylose, β-L-colitose, D-paratose and D-tyvelose. All five 3,6-dideoxyhexoses have been found in different serovars of Yersinia pseudotuberculosis, while other genera possess only some of them. For example, Salmonella enterica enterica serovar Typhimurium group B contains D-abequose, Salmonella enterica enterica serovar Paratyphi A str. ATCC 9150 contains D-paratose and Salmonella enterica enterica serovar Typhi contains D-tyvelose [Thorson94].
These sugars are synthesized via a complex series of enzymatic reactions starting, in most cases, from CDP-α-D-glucose, derived from α-D-glucopyranose 1-phosphate. In a reaction catalyzed by the NAD+-dependent CDP-D-glucose-4,6-dehydratase, CDP-α-D-glucose is converted to CDP-4-dehydro-6-deoxy-D-glucose, which is then converted to the intermediate CDP-4-dehydro-3,6-dideoxy-D-glucose in two consecutive enzymatic reactions, mediated by two components of the CDP-4-dehydro-6-deoxyglucose reductase enzyme complex. The first component is CDP-6-deoxy-L-threo-D-glycero-4-hexulose-3-dehydrase (E1), a pyridoxamine 5'-phosphate (PMP)-linked iron-sulfur-containing catalyst, while the second component is CDP-6-deoxy-L-threo-D-glycero-4-hexulose-3-dehydrase reductase (E3), a [2Fe-2S]-containing flavoprotein.
The product of this complex, CDP-4-dehydro-3,6-dideoxy-D-glucose, is the parent to all five 3,6-dideoxyhexoses.
About This Pathway
CDP-ascarylose, found in Yersinia pseudotuberculosis, is produced by the successive action of two enzymes: CDP-3, 6-dideoxy-D-glycero-D-glycero-4-hexulose-5-epimerase inverts the configuration of its substrate, CDP-4-dehydro-3,6-dideoxy-D-glucose, at carbon C-5, while CDP-3, 6-dideoxy-D-glycero-L-glycero-4-hexulose-4-reductase catalyzes a stereospecific reduction at carbon C-4, yielding CDP-ascarylose [Thorson93].
Thorson93: Thorson, J.S., Lo, S.F., Liu, H.W. (1993). "Molecular basis of 3,6-dideoxyhexose biosynthesis: elucidation of CDP-ascarylose biosynthetic genes and their relationship to other 3,6-dideoxyhexose pathways." J. Am. Chem. Soc. 115:5827-5828.
Thorson94: Thorson JS, Lo SF, Ploux O, He X, Liu HW (1994). "Studies of the biosynthesis of 3,6-dideoxyhexoses: molecular cloning and characterization of the asc (ascarylose) region from Yersinia pseudotuberculosis serogroup VA." J Bacteriol 176(17);5483-93. PMID: 8071227
Hallis98: Hallis TM, Lei Y, Que NL, Liu H (1998). "Mechanistic studies of the biosynthesis of paratose: purification and characterization of CDP-paratose synthase." Biochemistry 37(14);4935-45. PMID: 9538012
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