Purification of dextran-binding protein from cariogenic Streptococcus mutans

An extracellular protein produced by $\text{Streptococcus mutans}$ was purified to electrophoretic homogeneity by affinity chromatography on Sephadex G50 followed by gel filtration. The protein is devoid of both dextransucrase and dextranase activity but binds dextran and therefore probably is implicated in the adherence of $\text{S. mutans}$ cells to the host tooth surface. The presence of the dextran-binding protein may be a determinant of the pathogenicity of such cariogenic micro-organisms.