Induction of the Staphylococcal Proteolytic Cascade by Antimicrobial Fatty Acids in Community Acquired Methicillin Resistant Staphylococcus aureus
Figure 5
SDS-PAGE and Coomassie staining (A and C), or Western blot for detection of SspA (B, D and E), in cultures of S. aureus grown in TSB containing 0 or 25 µM linoleic acid (LA) as indicated.
Protein loading was 2.0 OD600 units for SDS-PAGE, and 0.02 OD600 units for Western blot. The S. aureus strains are defined in Table 1. Arrows and labels on the right margins of panels A and C indicate the location of 72 kDa glycerol ester hydrolase precursor (proGeh) and mature lipase (Geh), while arrows on the protein gels point to SspA protein that is induced in response to 25 µM LA. SspA exhibits some expected variation in size, being comprised of 327 amino acids in USA400 (MW_0932), 336 amino acids in USA300 (SAUSA300_0951), and 357 amino acids in MRSA252 (SAR_1022) and other CC30 strains, due to variation in a C-terminal disordered segment comprised of tripeptide repeats. Different isomers produced by the same strain as shown on Western blot (5E), and explained in the text, are attributed to varying degrees of processing of the N-terminal propeptide of the SspA precursor, proSspA.