Cloning and characterization of an alpha-enolase of the oral pathogen Streptococcus mutans that binds human plasminogen.

Streptococcus mutans is the etiologic agent of dental caries and is a causative agent of infective endocarditis. While the mechanisms by which S. mutans cells colonize heart tissue is not clear, it is thought that bacterial binding to extracellular matrix and blood components is crucial in the development of endocarditis. Previously, we have demonstrated that S. mutans cells have the capacity to bind and activate plasminogen to plasmin. Here we report the first cloning and characterization of an alpha-enolase of S. mutans that binds plasminogen. The functional identity of the purified recombinant alpha-enolase protein was confirmed by its ability to catalyze the conversion of 2-phosphoglycerate to phosphoenolpyruvate. The protein exhibited a Km of 9.5 mM and a Vmax of 31.0 mM/min/mg. The alpha-enolase protein was localized in the cytoplasmic, cell wall and extracellular fractions of S. mutans. Binding studies using an immunoblot analysis revealed that human plasminogen binds to the enolase enzyme of S. mutans. These findings identify S. mutans alpha-enolase as a binding molecule used by this oral pathogen to interact with the blood component, plasminogen. Further studies of this interaction may be critical to understand the pathogenesis of endocarditis caused by S. mutans.