Application of immunoproteomics to analysis of post‐translational processing of the antiphagocytic M protein of Streptococcus

Post‐translational modification of the antiphagocytic M1 protein of Streptococcus pyogenes can influence its binding properties for human immunoglobulin G subclasses and its invasive potential. Current methods of monitoring this modification event involve N ‐terminal sequencing and are cumbersome, slow and not amenable to routine analysis. In this study we demonstrate that surface enhanced laser desorption/ionization‐time of flight mass spectrometry can be used to monitor modification of the M1 protein by the secreted bacterial cysteine protease, SpeB. This method, when combined with a specific antibody capture step provides a specific, rapid and sensitive assay for key virulence factors of the important human pathogen Streptococcus pyogenes .