Purification and Immunochemical Properties of a Protein Antigen from Serotype g Streptococcus mutans

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Abstract
A proteinaceous antigen (PAg) was purified from the culture supernatant of Streptococcus mutans 6715 (serotype g) by ultrafiltration, ammonium sulfate precipitation, DEAE‐Sephacel ion‐exchange chromatography, Phenyl‐Sepharose CL‐4B hydrophobic chromatography, and subsequent Sephacryl S‐300 gel filtration. A yield of 0.1 mg of PAg was obtained from a liter of culture supernatant. The isoelectric point and molecular weight of PAg were pH 4.6 and 210,000, respectively. It contained 35% sugar, which was identified as glucose by gas‐liquid chromatography. Amino acid analysis revealed that PAg contains 28% acidic and 11% basic amino acid residues. PAg retained its antigenicity after heating at 80 C for 10 min in deionized water, or after treatment with 0.1 M HCl or 0.1 M NaOH at 37 C for 1 hr. Immunodiffusion and Immunoelectrophoresis analyses revealed that PAg is serologically distinct from other cell‐surface antigens such as serotype‐specific polysaccharide and lipoteichoic acid. A cross‐reaction between PAg and a protein antigen similarly prepared from serotype c S. mutans was observed in immunodiffusion tests.