Purification and characterization of an intracellular family 3 β-glucosidase from Lactobacillus sanfranciscensis CB1

Lactobacillus sanfranciscensis CB1 uses cellobiose and other β-glucosides (methyl-β-glucoside, arbutin, amygdalin and salicin) as carbon sources. A hexameric ca. 288 kDa β-glucosidase was purified to homogeneity from Lact. sanfranciscensis CB1 by four chromatographic steps. The enzyme was optimally active at pH 7.5 and 40°C. It had a pI of ca. 4.38 and a D_55°C value of ca. 27 sec. Almost total inhibition was found with sulfhydryl-modifying agents and divalent cations such as Cu²⁺, Co²⁺, Hg²⁺, Ni²⁺ and Fe²⁺ at a concentration of 2 mM. The enzyme was active towards β-(1→4) substrates such as p-nitrophenyl-β-D-glucoside, -D-galactoside and -L-rhamnoside, and cellobiose. The sequencing of four internal peptides showed an elevated identity with other bacterial β-glucosides of family 3. A PCR strategy with primers designed on the basis of conserved sequences was used to partially identify the gene. The deduced amino acid sequence showed 53, 48 and 45% identity with GHF3 from Ruminococcus albus, Clostridium thermocellum and Bifidobacteriam longum, respectively.