Monofluorophosphate inhibits the key step of internal polysaccharide biosynthesis in Streptococcus mutans

Abstract

Streptococcus mutans is the leading cause of dental caries worldwide and accumulates a glycogen‐like internal polysaccharide (IPS) which contributes to cariogenicity when grows in excess of sugars. Previously, we characterized the ADP‐glucose (ADP‐Glc) pyrophosphorylase (ADP‐Glc PPase; EC 2.7.7.27) from S. mutans, belonging to the key step leading to IPS synthesis. The enzyme showed two active conformations, homotetrameric GlgC and heterotetrameric GlgC/GlgD, the latter being one magnitude order more active and having different regulatory properties. Also, sodium monofluorophosphate (MFP) is the toothpastes active compound with established anticariogenic properties, although the molecular target and/or its mechanism are still unknown. In this work, we show that MFP partially inhibits (up to a 70% inhibition) both ADP‐Glc PPase active conformations, with I0.5 values of 1.5 mM and 8 mM for GlgC/GlgD and GlgC, respectively. Interestingly, MFP completely inhibited (with an I0.5 3.2 mM) a Fru‐1,6‐bisP activated GlgC form. Controls with NaF up to 25 mM were conducted and no inhibitions were observed neither in GlgC nor GlgC/GlgD. The inhibition of ADP‐Glc PPase was correlated with in vivo studies showing a decreased IPS accumulation in S. mutans cultures in the presence of 2 mM MFP. Other in vivo implications of MFP concern decreases in lactate production, acidogenesis and bacterial growth. Considering that synthesis of glycogen occurs by different pathways in mammals and bacteria, it is worth to highlight that ADP‐Glc PPase can be visualized as a particular target for controlling S. mutans virulence by means of MFP. Supported by funds from Colgate‐Palmolive (CN and MAB), NSF MCB‐1024945 (MAB), and CONICET [PIP 2519], UNL [CAI‐Orientado and Redes] and ANPCyT [PICT’08 1754] (AAI)