Xylose isomerase (EC 18.104.22.168)  is an enzyme found in microorganisms which
catalyzes the interconversion of an aldo sugar D-xylose to a keto sugar
D-xylulose. It can also isomerize D-ribose to D-ribulose and D-glucose to
D-fructose. Xylose isomerase seems to require magnesium for its activity,
while cobalt is necessary to stabilize the tetrameric structure of the enzyme.
Xylose isomerase also exists in plants  where it is manganese-dependent.
The enzyme has also been found in anaerobic fungi .
A number of residues are conserved in all known xylose isomerases. A histidine
in the N-terminal section of the enzyme has been shown  to be involved in
the catalytic mechanism of the enzyme. Two glutamate residues, a histidine and
four aspartate residues are the metal-binding sites that bind two ions of
magnesium, cobalt, or manganese [5,6,7].
Three-dimensional structures of xylose isomerases show a that each subunit
contains a common α/β-barrel fold (see <PDB:2GLK; A>)  similar to
that of other divalent metal-dependent TIM barrel enzymes, such as rhamnose
isomerase  and endonuclease 4 (see <PDOC00599>) [1,5,6]. The C-terminal
smaller part forms an extended helical fold that seems to be implicated in
We have developed a profile that covers the entire xylose isomerase structure.
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