B6db activities : cold

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	ColD
Description	GDP-4-keto-6-deoxy-D-mannose-3-dehydratase (4.3.1.-)
Alternative names	GDP-4-oxo-6-deoxy-D-mannose-3-dehydratase
Catalyzed reaction	GDP-4-oxo-6-deoxy-D-mannose + L-glutamate = GDP-4-oxo-3,6-dideoxy-D-mannose + 2-oxoglutarate + NH3
Cofactor	Pyridoxal-phosphate
Comments	The overall reaction proposedly includes (i) a half-transamination, in which glutamate reacts with PLP, generating oxoglutarate and PMP. (ii) Condensation of PMP with GDP-4-keto-6-deoxy-D-mannose, to yield the respective ketoimine. (iii) elimination of the 3-hydroxy group from the mannose moyety, with formation of the external aldimine of GDP-6-deoxy-4-amino-delta(3,4)-mannooseen (iv) hydrolysis of the aldimine linkage (regenerating PLP) and hydration of the double bond in the mannoseen ring, releasing ammonia and yielding the final carbohydrate product, GDP-4-keto-3,6-dideoxy-D-mannose
	The enzyme is involved in the biosynthesis of colitose, a 3,6-dideoxysugar that has been isolated from 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. This enzyme is related to the E1 protein of CDP-4-dehydro-6-deoxyglucose reductase (EC 1.17.1.1) and shares with the latter the absence of an active site lysine - meaning that PLP is not covalently bound to the enzyme through an internal aldimine linkage.
PDB	2GMS; 2GMU;
Organisms	-Bacteria
Family	cold (5)

Links	Enzyme (activities) ColD BRENDA (activities) ColD KEGG (pathways) ColD PLPMDB (PLP mutants) ColD

References	Cook, P.D.; Thoden, J.B.; Holden, H.M. (2006) The structure of GDP-4-keto-6-deoxy-D-mannose-3-dehydratase: a unique coenzyme B6-dependent enzyme Protein Sci 15 2093-106.. Alam J, Beyer N, Liu HW. (2004) Biosynthesis of colitose: expression, purification, and mechanistic characterization of GDP-4-keto-6-deoxy-D-mannose-3-dehydrase (ColD) and GDP-L-colitose synthase (ColC). Biochemistry 43 16450-60. . Articles on cold

last changed	2009/01/08 13:29

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