The Streptococcus pneumoniae beta-galactosidase is a surface protein

The beta-galactosidase gene of Streptococcus pneumoniae, bgaA, encodes a pu tative 2,235-amino-acid protein with the two amino acid motifs characterist ic of the glycosyl hydrolase family of proteins. In addition, an N-terminal signal sequence and a C-terminal LPXTG motif typical of surface-associated proteins of gram-positive bacteria are present. Trypsin treatment of cells resulted in solubilization of the enzyme, documenting that it is associate d with the cell envelope. In order to obtain defined mutants suitable for l acZ reporter experiments, the bgaA gene was disrupted, resulting in a compl ete absence of endogenous beta-galactosidase activity. The results are cons istent with beta-galactosidase being a surface protein that seems not to be involved in lactose metabolism but that may play a role during pathogenesi s.