DEVELOPMENT OF A RADIOACTIVE PROTEIN A-BASED ASSAY FOR ANALYSIS OF SURFACE PROTEIN EXPRESSION IN GRAM-POSITIVE BACTERIA

This paper describes an immunochemical method which uses radioactive p rotein A for the detection and analysis of streptococcal M6 protein ep itopes on the surface of recombinant Streptococcus gordonii. With this assay, recombinant S. gordonii cells expressing a portion of the M6 p rotein on their surfaces show a 75-fold increase in bound radioactivit y over cells of the control S. gordonii parental strain. Furthermore, use of the assay to monitor the amount of M6 protein present on the su rface of the S. gordonii recombinant during growth in culture demonstr ated that expression is highest at late log phase, with the protein be ing sloughed off during stationary phase. This simple assay allows ana lysis of surface protein without any protein purification or sophistic ated instrumentation. As such, it should be broadly applicable to foll owing the expression of most surface accessible bacterial proteins.