The Streptococcus pneumoniae beta-galactosidase is a surface protein - PubMed (original) (raw)

Comparative Study

The Streptococcus pneumoniae beta-galactosidase is a surface protein

D Zähner et al. J Bacteriol. 2000 Oct.

Abstract

The beta-galactosidase gene of Streptococcus pneumoniae, bgaA, encodes a putative 2,235-amino-acid protein with the two amino acid motifs characteristic 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 associated with the cell envelope. In order to obtain defined mutants suitable for lacZ reporter experiments, the bgaA gene was disrupted, resulting in a complete absence of endogenous beta-galactosidase activity. The results are consistent with beta-galactosidase being a surface protein that seems not to be involved in lactose metabolism but that may play a role during pathogenesis.

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Figures

FIG. 1

FIG. 1

Schematic representation of the β-galactosidase of_S. pneumoniae_ (S.p.). The amino acid (aa) sequences are given for three important regions: the N-terminal signal peptide (residues 1 to 55; the arrow marks the putative signal peptidase cleavage site); the two conserved motifs of glycosyl hydrolase family 2 (hatched boxes) within the region homologous to other β-galactosidases (stippled box; approximately residues 90 to 600); and 35 C-terminal residues with the cell wall-anchoring LPXTG motif (stippled box at right end). The putative active site is aligned with β-galactosidases of the following organisms: S.t., S. thermophilus (SWISS-PROT P23989); T.e., Thermoanaerobacter ethanolicus (SWISS-PROT P77989); L.d., Lactobacillus delbrueckii (SWISS-PROT P33486); and E. coli (GenBank AJ002684). Strictly conserved amino acid residues within the motifs are highlighted. The C-terminal region is compared to those of other proteins containing an LPXTG motif: M-protein, S. pyogenes M protein (PIR S30283); S. pneumoniae proteins NanA (neuraminidase A; SWISS-PROT 59959), StrH (β-_N_-acetylglucosaminidase; SWISS-PROT P49610), and Hya (hyaluronidase; SWISS-PROT Q54873). Dots indicate gaps in the alignment; the asterisk marks the C terminus.

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