Role of group A Streptococcus HtrA in the maturation of SpeB protease

The serine protease HtrA (DegP) of the human pathogen Streptococcus pyogenes (group A Streptococcus; GAS) is localized to the ExPortal secretory microdomain and is reportedly essential for the maturation of cysteine protease SpeB. Here we utilize HSC5 (M5 serotype) and the in-frame isogenic mutant HSC5ΔhtrA to determine whether HtrA contributes to the maturation of other GAS virulence determinants. Mutanolysin cell wall extracts and secreted proteins were arrayed by 2-DE and identified by MALDI-TOF PMF analysis. HSC5ΔhtrA had elevated levels of cell wall-associated M protein, whilst the supernatant had higher concentrations of M protein fragments and a reduced amount of mature SpeB protease, compared to wild-type. Western blot analysis and protease assays revealed a delay in the maturation of SpeB in the HSC5ΔhtrA supernatant. HtrA was unable to directly process SpeB zymogen to the active form in vitro. We therefore conclude that HtrA plays an indirect role in the maturation of cysteine protease SpeB.