Methods: SDS-PAGE was used to separate membrane proteins extracted from S. mutans UA159, cultured in the presence and absence of 5 mM sodium fluoride. Liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to identify proteins in conjunction with interrogation of the S. mutans translated genomic database.
Results: Proteins containing up to 10 predicted transmembrane domains were detected in the S. mutans membrane sub-proteome. Preliminary data suggest that expression of a number of S. mutans membrane proteins are altered in bacteria cultured in the presence of fluoride. Proteins with a putative role in bacitracin synthesis and stress response were up-regulated in bacteria exposed to fluoride. Differential expression of some key S. mutans virulence determinants was also demonstrated.
Conclusion: Membrane proteins fulfil a wide range of important biological functions but are often greatly under-represented in proteomic analyses using two-dimensional gel electrophoresis. A combination of SDS-PAGE and LC-MS/MS has allowed the most comprehensive description of the S. mutans membrane sub-proteome to date. Growth in the presence of fluoride affects the expression of many S. mutans proteins in addition to enolase and the H+-ATPase. This in turn may affect the ability of S. mutans to cause dental caries.
Funded by a BBSRC/GlaxoSmithKline CASE award.