Xylose isomerase (EC 5.3.1.5) [1] 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 [2] where it is manganese-dependent.
The enzyme has also been found in anaerobic fungi [3].
A number of residues are conserved in all known xylose isomerases. A histidine
in the N-terminal section of the enzyme has been shown [4] 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>) [7] similar to
that of other divalent metal-dependent TIM barrel enzymes, such as rhamnose
isomerase [8] and endonuclease 4 (see <PDOC00599>) [1,5,6]. The C-terminal
smaller part forms an extended helical fold that seems to be implicated in
multimerization.
We have developed a profile that covers the entire xylose isomerase structure.
Structures of D-xylose isomerase from Arthrobacter strain B3728 containing the inhibitors xylitol and D-sorbitol at 2.5 A and 2.3 A resolution, respectively.
Crystal structures of thermostable xylose isomerases from Thermus caldophilus and Thermus thermophilus: possible structural determinants of thermostability.
The structure of rhamnose isomerase from Escherichia coli and its relation with xylose isomerase illustrates a change between inter and intra-subunit complementation during evolution.
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