ClpXP Degrades SsrA-Tagged Proteins inStreptococcus pneumoniae

Abstract

Bacterial proteins that are abnormally truncated due to incomplete mRNA or the presence of rare codons are extended by an SsrA tag during ribosome rescue in a trans-translation process important for maintaining protein quality. In Escherichia coli, the SsrA-tagged proteins become the target of the Tsp, Lon, FtsH, ClpXP, and ClpAP proteases. Here we show that degradation of model SsrA-tagged proteins in Streptococcus pneumoniae depends primarily or exclusively on ClpXP in vivo. In addition, we show the E. coli SsrA tag is also a target of S. pneumoniae ClpXP in vivo, even though the N-terminal portions of the tags differ significantly between the two species, suggesting there may be no adaptor protein for SsrA in S. pneumoniae.

Degradation of SsrA-tagged proteins in streptococci

“…2a, b), indicating that ClpP played a core role in the proteolysis of SsrA-tagged proteins. However, we expected that a similar pattern would be observed in the DclpX strain, as ClpA was absent and ClpXP was the only the known proteolytic complex for the degradation of SsrA-tagged proteins in streptococci (Ahlawat & Morrison, 2009). Surprisingly, although significant amounts of GFPssrA and GFPavaa proteins were still present in the DclpX strain, they were drastically reduced (Fig.…”

“…ClpXP degrades SsrA-tagged proteins in S. mutans, and the complex formation between ClpX and ClpP is essential for the degradation It was previously reported that ClpXP was responsible for SsrA-tagged protein degradation in Gram-positive bacteria such as B. subtilis and S. pneumoniae (Ahlawat & Morrison, 2009;Wiegert & Schumann, 2001). To determine whether ClpXP also degraded SsrA-tagged proteins in S. mutans, a sequence encoding S. mutans SsrA tag was added to the Cterminal of the GFP.…”

“…Similarly, the genus Streptococcus does not encode ClpA, Lon and Tsp proteases. A previous study showed that only ClpXP degrades SsrA-tagged proteins in S. pneumoniae (Ahlawat & Morrison, 2009). Although FtsH is present in S. pneumoniae, this protease does not play a role in the degradation of SsrAtagged proteins in this organism (Ahlawat & Morrison, 2009).…”

“…A previous study showed that only ClpXP degrades SsrA-tagged proteins in S. pneumoniae (Ahlawat & Morrison, 2009). Although FtsH is present in S. pneumoniae, this protease does not play a role in the degradation of SsrAtagged proteins in this organism (Ahlawat & Morrison, 2009). In the present study, we also found that ClpXP is the major protease complex responsible for the degradation of SsrA-tagged proteins in S. mutans.…”

“…In Gram-positive bacteria such as Bacillus subtilis and Streptococcus pneumoniae, ClpXP is the only known protease that degrades SsrA-tagged proteins (Ahlawat & Morrison, 2009;Wiegert & Schumann, 2001). Most of the Firmicutes, including Bacillus and Streptococcus, do not encode ClpA; rather, they encode two other AAA+ proteins, ClpC and ClpE.…”