β-Glucoside metabolism in Oenococcus oeni: Cloning and characterization of the phospho-β-glucosidase CelD

In previous work, we reported characterization of a phospho-β-glucosidase gene bglD in a β-glucoside metabolizing operon in the oenologically important lactic acid bacterium Oenococcus oeni. Here we report a second phospho-β-glucosidase gene celD which has been cloned and expressed in Escherichia coli. This gene is found in a putative operon 6043 bp long encoding six genes designated celA to celF. Comparative sequence analyses of lactic acid bacteria suggest that the open reading frames of celA, B and F from the sequenced O. oeni PSU-1 encode phosphoenolpyruvate dependent phosphotransferase system (PEP-PTS) components IIB, IIA and IIC, respectively, which regulate the uptake and phosphorylation of β-glucosides across the cytoplasmic membrane. celE is speculated to have a regulatory function. celD was cloned and expressed in E. coli followed by purification of the gene product. The purified protein His-tagged CelD (485 residues, Mw = 55.8 kDa) has high homology to known phospho-β-glucosidases and has high activity towards the phosphorylated β-glucoside para-nitrophenol-β-d-glucopyranoside-6-phophate (pNPβG6P). CelD has an optimum pH between 4.0 and 5.0 and is most active at 40 °C. The gene celC was cloned, heterologously expressed and purified (481 residues, Mw = 55.7 kDa) but showed no significant activity towards pNPβG6P despite high sequence homology to celD and characterized phospho-β-glucosidases. Neither CelC nor CelD are active against non-phosphorylated β-glucosides.