Acta Cryst. (2013). D69, 451-463 [ doi:10.1107/S0907444912049608 ]
Abstract: In lactic acid bacteria and other bacteria, carbohydrate uptake is mostly governed by phosphoenolpyruvate-dependent phosphotransferase systems (PTSs). PTS-dependent translocation through the cell membrane is coupled with phosphorylation of the incoming sugar. After translocation through the bacterial membrane, the -glycosidic bond in 6'-P--glucoside is cleaved, releasing 6-P--glucose and the respective aglycon. This reaction is catalyzed by 6-P--glucosidases, which belong to two glycoside hydrolase (GH) families: GH1 and GH4. Here, the high-resolution crystal structures of GH1 6-P--glucosidases from Lactobacillus plantarum (LpPbg1) and Streptococcus mutans (SmBgl) and their complexes with ligands are reported. Both enzymes show hydrolytic activity towards 6'-P--glucosides. The LpPbg1 structure has been determined in an apo form as well as in a complex with phosphate and a glucose molecule corresponding to the aglycon molecule. The S. mutans homolog contains a sulfate ion in the phosphate-dedicated subcavity. SmBgl was also crystallized in the presence of the reaction product 6-P--glucose. For a mutated variant of the S. mutans enzyme (E375Q), the structure of a 6'-P-salicin complex has also been determined. The presence of natural ligands enabled the definition of the structural elements that are responsible for substrate recognition during catalysis.
PDB references: 3qom, 4gze, 3pn8, 4f66 and 4f79
Keywords: 6-P--glucosidases; glycoside hydrolases; GH1; cellobiose; gentiobiose; salicin.
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