Identification of protein differences between two clinical isolates of Streptococcus mutans by proteomic analysis

Streptococcus mutans is generally considered to be the principal etiological agent for dental caries. Different strains of S. mutans may display different virulence mechanisms, so the isolation of the differential proteins is illuminating.

S. mutans strains 9-1 and 9-2, which both colonized the same oral cavity, were selected after screening for the possession of suspected virulence traits. The soluble cellular proteins were extracted from steady-state planktonic cells of strains 9-1 and 9-2 and were analyzed using high-resolution two-dimensional gel electrophoresis. Then, replicate maps of proteins from the two strains were generated. Proteins expressed only in strain 9-1 or 9-2 were excised and digested with trypsin by using an in-gel protocol. Tryptic digests were analyzed using matrix-assisted laser desorption/ionization time of flight mass spectrometry, by which peptide mass fingerprints were generated, and these were used to assign putative functions according to their homology with the translated sequences in the S. mutans genomic database.

There were 12 proteins only expressed in strain 9-1 and three proteins only expressed in strain 9-2. They were involved in protein biosynthesis, protein folding, cell wall biosynthesis, fatty acid biosynthesis, nucleotide biosynthesis, repair of DNA damage, carbohydrate metabolism, signal transduction, and translation.

The identification of proteins differentially expressed between strains 9-1 and 9-2 provides new information concerning the mechanisms of cariogenesis