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The sugar isomerase (SIS) domain is a phosphosugar-binding module that is
found in a variety of eubacterial, archaebacterial and eukaryotic proteins
that have a role in phosphosugar isomerization or regulation . In enzymes,
the SIS domain can have a catalytic function as an isomerase and bind to
phosphorylated sugars. In bacterial transcriptional regulators of the rpiR
family, the domain seems to bind substrates implicated in the genes for sugar
metabolism that are controlled by the regulator. The SIS domain is found in
one or two copies and can be linked to additional domains, such as
helix-turn-helix (HTH) (see <PDOC51071>), CBS (see <PDOC51371>), glutamine
amidotransferases type 2 (see <PDOC00406>), or phosphopantetheine-attachment
(see <PDOC00012>) [1,2].
The SIS domain has an α-β structure and is dominated by a five-stranded
parallel β sheet flanked on either side by α helices forming a three-layer α-β-α sandwich (see <PDB:1MOQ>) . The fold shows
similarities to that of glucose-6-phosphate isomerase (see <PDOC00157>).
Some proteins known to contain a SIS domain are listed below:
Eukaryotic and prokaryotic glucosamine--fructose-6-phosphate
aminotransferase [isomerizing] (EC 188.8.131.52).
Eukaryotic glucokinase regulator (GCKR) family (see <PDOC00979>).
Bacterial rpiR family of HTH transcriptional regulators (see <PDOC51071>).
Enterobacterial dnaA initiator-associating protein diaA.
Proteobacterial N-acetylmuramic acid 6-phosphate etherase (murQ)
(EC 4.2.-.-), which catalyzes the cleavage of the D-lactyl ether
substituent of MurNAc 6-phosphate, producing GlcNAc 6-phosphate and
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