Isolation of a novel protein involved in the transport of fructose by an inducible phosphoenolpyruvate fructose phosphotransferase system in Streptococcus mutans

Abstract

Fructose transport in Streptococcus mutans LG-1 is mediated by at least two distinct phosphoenolpyruvate fructose phosphotransferase systems. One system is constitutive and consists of membrane components enzyme II as well as enzyme I and heat-stable protein. The other system is inducible and requires, in addition to enzyme I and heat-stable protein, a soluble substrate-specific protein for catalytic activity. This protein factor, designated III(fru), was purified by DEAE-cellulose chromatography, hydroxylapatite chromatography, molecular sieving on Sephadex G-75, and preparative electrophoresis. The purified preparation showed only one protein band, with a molecular weight of 12,600, on sodium dodecyl sulfate-urea-polyacrylamide gel electrophoresis, on gel electrophoresis with the discontinuous buffer Tris-glycine, and after electrofocusing in gel (pI ≃ 3.7). The molecular weight of the native protein determined by gel filtration at 4°C was 51,000. Immunodiffusion experiments performed with immunoglobulins prepared against the purified III(fru) from S. mutans LG-1 suggested that other S. mutans strains possessed a III(fru). No precipitin bands, however, were detected with extracts from S. salivarius, S. sanguis, S. lactis, S. faecalis, Staphylococcus aureus, Bacillus subtilis, Lactobacillus casei, and Escherichia coli.