InterPro domain: IPR001347

The sugar isomerase (SIS) domain is a phosphosugar-binding module that isfound in a variety of eubacterial, archaebacterial and eukaryotic proteinsthat have a role in phosphosugar isomerization or regulation [ 1 ]. In enzymes,the SIS domain can have a catalytic function as an isomerase and bind tophosphorylated sugars. In bacterial transcriptional regulators of the rpiRfamily, the domain seems to bind substrates implicated in the genes for sugarmetabolism that are controlled by the regulator. The SIS domain is found inone or two copies and can be linked to additional domains, such ashelix-turn-helix (HTH), CBS, glutamineamidotransferases type 2, or phosphopantetheine-attachment [ 2 , 2 ].

The SIS domain has an alpha-beta structure and is dominated by a five-strandedparallel beta sheet flanked on either side by alpha helices forming a three-layer alpha-beta-alpha sandwich [ 3 ]. The fold showssimilarities to that of glucose-6-phosphate isomerase.

1. The SIS domain: a phosphosugar-binding domain. Trends Biochem. Sci. 24, 94-5
2. N-acetylmuramic acid 6-phosphate lyases (MurNAc etherases): role in cell wall metabolism, distribution, structure, and mechanism. Cell. Mol. Life Sci. 65, 928-39
3. Involvement of the C terminus in intramolecular nitrogen channeling in glucosamine 6-phosphate synthase: evidence from a 1.6 A crystal structure of the isomerase domain. Structure 6, 1047-55