The ADP-glucose pyrophosphorylase from Streptococcus mutans provides evidence for the regulation of polysaccharide biosynthesis in Firmicutes.

ASENCION DIEZ MATÏAS; DEMONTE AM; GUERRERO SA; BALLICORA MA; IGLESIAS, AA

MOLECULAR MICROBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2013 vol. 90 p. 1011 - 1027

0950-382X

Streptococcus mutans is the leading cause of dental caries worldwide. The bacterium accumulates a glycogen-like internal polysaccharide, which mainly contributes to its carionegic capacity. S. mutans has two genes (glgC and glgD) respectively encodingputative ADP-glucose pyrophosphorylases (ADP-Glc PPase), a key enzyme for glycogen synthesis in most bacteria. Herein, we report the molecular cloning and recombinant expression of both genes (separately or together) followed by the characterization of therespective enzymes. When expressed individually GlgC had ADP-Glc PPase activity, whereas GlgD was inactive. Interestingly, the coexpressed GlgC/GlgD protein was one order of magnitude more active than GlgC alone. Kinetic characterization of GlgC and GlgC/GlgD pointed out remarkable differences between them. Fructose-1,6-bis-phosphate activated GlgC by twofold, but had no effect on GlgC/GlgD. Conversely, phospho-enol-pyruvate and inorganic salts inhibited GlgC/GlgD without affecting GlgC. However, inthe presence of fructose-1,6-bis-phosphate GlgC acquired a GlgC/GlgD-like behaviour, becoming sensitive to the stated inhibitors. Results indicate that S. mutans ADP-Glc PPase is an allosteric regulatory enzyme exhibiting sensitivity to modulation by keyintermediates of carbohydrates metabolism in the cell. The particular regulatory properties of the S. mutans enzyme agree with phylogenetic analysis, where GlgC and GlgD proteins found in other Firmicutes arrange in distinctive clusters.