Molecular cloning and sequencing of two phospho-β-galactosidase I and II genes of lactobacillus gasseri JCM1031 isolated from human intestine

Lactobacillus (Lb.) gasseri JCM1031, which is classified into the B₁ subgroup of the Lb. acidophilus group of lactic acid bacteria, characteristically produces two different phospho-β-galactosidases (P-β-gal) I and II in the same cytosol as reported in our previous papers [Biosci. Biotech. Biochem., 60, 139-141, 708-710 (1996)]. To clarify the functional and genetic properties of the two enzymes, the structural genes of P-β-gal I and II were cloned and sequenced. The structural gene of P-β-gal I had 1,446 bp, encoding a polypeptide of 482 amino acid residues. The structural gene of P-β-gal II had 1,473 bp, encoding a polypeptide of 491 amino acid residues. The deduced relative molecular masses of 55,188 and 56,243 agreed well with the previous value obtained from the purified P-β-gal I and II protein, respectively. Multiple alignment of the protein sequence of P-β-gal I and II with those of P-β-gals from 5 microorganisms had 30-35% identity on the amino acid level, but those with phospho-β-glucosidases from 5 microorganisms had the relatively high identity of about 50%. Considering that this strain grows on lactose medium and shows no β-galactosidase activity, and that purified P-β-gal I and II can obviously hydrolyze o-nitrophenyl-β-D-galactopyranoside 6-phosphate (substrate), and also the conservation of a cysteine residue in the molecule, the P-β-gal I and II were each confirmed as a novel P-β-gal enzyme.