β-Glucoside metabolism in Oenococcus oeni: Cloning and characterisation of the phospho-β-glucosidase bglD

The structural gene for a phospho-β-glucosidase from the oenologically important lactic acid bacterium (LAB) Oenococcus oeni has been cloned and its protein product characterised. This gene is found in a putative β-glucosidase operon of 2178 base pairs encoding 4 genes designated bglA to bglD. The bglA, B and C genes were not cloned and characterised, however, are thought to be phosphoenolpyruvate dependent phospho transferase system (PEP-PTS) components IIC, IIA and IIB which regulate the uptake, phosphorylation and translocation of β-glucosides across the cytoplasmic membrane. The cloned bglD was sequenced and expressed in Escherichia coli followed by purification. The purified bglD protein has 480 residues, a molecular mass of 55.5 kDa and shows high homology to known phospho-β-glucosidases. bglD exhibited high activity towards the phosphorylated β-glucoside para-nitrophenol-β-d-glucopyranoside-6-phosphate with a pH optimum of 5.5 and maintained similar levels of activity between temperatures of 4 °C and 40 °C. The enzyme was not active against non-phosphorylated β-glucosides.