Enzymes
| UniProtKB help_outline | 1,221 proteins |
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- Name help_outline aldehydo-D-galactose 6-phosphate Identifier CHEBI:58255 Charge -2 Formula C6H11O9P InChIKeyhelp_outline VFRROHXSMXFLSN-KCDKBNATSA-L SMILEShelp_outline [H]C(=O)[C@H](O)[C@@H](O)[C@@H](O)[C@H](O)COP([O-])([O-])=O 2D coordinates Mol file for the small molecule Search links Involved in 1 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
- Name help_outline keto-D-tagatose 6-phosphate Identifier CHEBI:134283 Charge -2 Formula C6H11O9P InChIKeyhelp_outline GSXOAOHZAIYLCY-PBXRRBTRSA-L SMILEShelp_outline [C@H](O)([C@@H](COP([O-])([O-])=O)O)[C@H](O)C(=O)CO 2D coordinates Mol file for the small molecule Search links Involved in 4 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
Cross-references
| RHEA:13033 | RHEA:13034 | RHEA:13035 | RHEA:13036 | |
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| Reaction direction help_outline | undefined | left-to-right | right-to-left | bidirectional |
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Publications
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Crystal structure and substrate specificity of D-galactose-6-phosphate isomerase complexed with substrates.
Jung W.S., Singh R.K., Lee J.K., Pan C.H.
D-Galactose-6-phosphate isomerase from Lactobacillus rhamnosus (LacAB; EC 5.3.1.26), which is encoded by the tagatose-6-phosphate pathway gene cluster (lacABCD), catalyzes the isomerization of D-galactose-6-phosphate to D-tagatose-6-phosphate during lactose catabolism and is used to produce rare s ... >> More
D-Galactose-6-phosphate isomerase from Lactobacillus rhamnosus (LacAB; EC 5.3.1.26), which is encoded by the tagatose-6-phosphate pathway gene cluster (lacABCD), catalyzes the isomerization of D-galactose-6-phosphate to D-tagatose-6-phosphate during lactose catabolism and is used to produce rare sugars as low-calorie natural sweeteners. The crystal structures of LacAB and its complex with D-tagatose-6-phosphate revealed that LacAB is a homotetramer of LacA and LacB subunits, with a structure similar to that of ribose-5-phosphate isomerase (Rpi). Structurally, LacAB belongs to the RpiB/LacAB superfamily, having a Rossmann-like αβα sandwich fold as has been identified in pentose phosphate isomerase and hexose phosphate isomerase. In contrast to other family members, the LacB subunit also has a unique α7 helix in its C-terminus. One active site is distinctly located at the interface between LacA and LacB, whereas two active sites are present in RpiB. In the structure of the product complex, the phosphate group of D-tagatose-6-phosphate is bound to three arginine residues, including Arg-39, producing a different substrate orientation than that in RpiB, where the substrate binds at Asp-43. Due to the proximity of the Arg-134 residue and backbone Cα of the α6 helix in LacA to the last Asp-172 residue of LacB with a hydrogen bond, a six-carbon sugar-phosphate can bind in the larger pocket of LacAB, compared with RpiB. His-96 in the active site is important for ring opening and substrate orientation, and Cys-65 is essential for the isomerization activity of the enzyme. Two rare sugar substrates, D-psicose and D-ribulose, show optimal binding in the LacAB-substrate complex. These findings were supported by the results of LacA activity assays. << Less
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Molecular cloning, characterization, and nucleotide sequence of the tagatose 6-phosphate pathway gene cluster of the lactose operon of Lactococcus lactis.
van Rooijen R.J., van Schalkwijk S., de Vos W.M.
The tagatose 6-phosphate pathway gene cluster (lacABCD) encoding galactose-6-phosphate isomerase, tagatose-6-phosphate kinase, and tagatose-1,6-diphosphate aldolase of Lactococcus lactis subsp. lactis MG1820 has been characterized by cloning, nucleotide sequence analysis, and enzyme assays. Transc ... >> More
The tagatose 6-phosphate pathway gene cluster (lacABCD) encoding galactose-6-phosphate isomerase, tagatose-6-phosphate kinase, and tagatose-1,6-diphosphate aldolase of Lactococcus lactis subsp. lactis MG1820 has been characterized by cloning, nucleotide sequence analysis, and enzyme assays. Transcription studies showed that the four tagatose 6-phosphate pathway genes are the first genes of the lactose-inducible lactose-phosphotransferase operon consisting of the lacABCDFEGX genes. Using a T7 expression system, it could be shown that the lacA, lacB, lacC, and lacD genes code for proteins with apparent molecular masses of 15, 19, 33, and 36 kDa, respectively. Cell-free extracts of induced and noninduced Escherichia coli cells expressing the lacABCD genes were used to determine the functions of the encoded proteins. Expression of both lacA and lacB was required to obtain galactose-6-phosphate isomerase activity. The lacC gene codes for tagatose-6-phosphate kinase, the deduced amino sequence of which is similar to that of E. coli Pfk-2 phosphofructokinase, and Staphylococcus aureus LacC protein. The tagatose-1,6-diphosphate aldolase is encoded by the lacD gene, and its deduced primary sequence, which is homologous to that of the S. aureus LacD protein, predicts an amino acid composition which is virtually identical to that of the previously purified L. lactis E8 tagatose-1,6-diphosphate aldolase. << Less
J. Biol. Chem. 266:7176-7181(1991) [PubMed] [EuropePMC]
This publication is cited by 3 other entries.