Colitose

Colitose is a mannose-derived 3,6-dideoxysugar produced by certain bacteria. It is a constituent of the lipopolysaccharide.^[1] It is the enantiomer of abequose.

Colitose

Names
IUPAC name 3,6-Dideoxy-L-xylo-hexose
Systematic IUPAC name (2S,4S,5S)-2,4,5-Trihydroxyhexanal
Identifiers
CAS Number	4221-05-0 Y
3D model (JSmol)	Interactive image
ChemSpider	5256780 N
PubChem CID	6857442
CompTox Dashboard (EPA)	DTXSID80962374
InChI InChI=1S/C6H12O4/c1-4(8)6(10)2-5(9)3-7/h3-6,8-10H,2H2,1H3/t4-,5-,6-/m0/s1 N Key: GNTQICZXQYZQNE-ZLUOBGJFSA-N N InChI=1/C6H12O4/c1-4(8)6(10)2-5(9)3-7/h3-6,8-10H,2H2,1H3/t4-,5-,6-/m0/s1 Key: GNTQICZXQYZQNE-ZLUOBGJFBL
SMILES O=C[C@@H](O)C[C@H](O)[C@@H](O)C
Properties
Chemical formula	C6H12O4
Molar mass	148.158 g·mol−1
Density	1.25 g/mL
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Biological role

Colitose is found in the O-antigen of certain Gram-negative bacteria such as Escherichia coli, Yersinia pseudotuberculosis, Salmonella enterica, Vibrio cholerae, and in marine bacteria such as Pseudoalteromonas sp.^[1][2] The sugar was first isolated in 1958,^[3] and subsequently was enzymatically synthesized in 1962.^[4]

Biosynthesis

The GDP-L-colitose biosynthesis pathway. For clarity, groups modified by the previous enzymatic step are highlighted in yellow.

The biosynthesis of colitose begins with ColE, a mannose-1-phosphate guanylyltransferase that catalyzes the addition of a GMP moiety to mannose, yielding GDP-mannose. In the next step, ColB, an NADP-dependent short-chain dehydrogenase-reductase enzyme, catalyzes the oxidation at C-4 and the removal of the hydroxyl group at C-6. The resulting product, GDP-4-keto-6-deoxymannose, then reacts with the PLP-dependent enzyme GDP-4-keto-6-deoxymannose-3-dehydratase (ColD), which removes the hydroxyl at C-3 in a manner similar to that of serine dehydratase. In the final step, the product of ColD, GDP-4-keto-3,6-dideoxymannose, reacts with ColC, which reduces the ketone functionality at C-4 back to an alcohol and inverts the configuration about C-5.^[5]

The resulting product, GDP-L-colitose, is then incorporated into the O-antigen by glycosyltransferases and O-antigen processing proteins. Further reactions join the O-antigen to the core polysaccharide to form the full lipopolysaccharide.

GDP-4-keto-6-deoxymannose-3-dehydratase (ColD)

ColD is a PLP-dependent enzyme responsible for the removal of the C-3' hydroxyl group during the biosynthesis of GDP-colitose.^[5] It is a product of the Wbdk or ColD genes in Escherichia coli O55 or Salmonella enterica, respectively, and is commonly referred to as ColD.^[1]

Usage in biotechnology

Although the sugar is relatively rare, recent work with glycosyltransferases suggests that obscure sugars such as colitose can be incorporated into existing natural-product scaffolds, thereby constructing novel and potentially therapeutic compounds.^[6]