A link between STK signalling and capsular polysaccharide synthesis in Streptococcus suis

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Capsular polysaccharide (CPS) is a key virulence factor in pathogenic bacteria like Streptococcus.
• CPS synthesis is regulated by the CpsBCD phosphoregulatory system.
• Serine/threonine kinases (STKs) also influence CPS synthesis, but the mechanisms are not fully understood.

Purpose of the Study:

• To elucidate the mechanism by which STKs regulate CPS synthesis in Streptococcus.
• To identify proteins linking STKs to the CpsBCD pathway.

Main Methods:

• Protein identification and phosphorylation analysis.
• Enzyme activity assays.
• Crystal structure determination of CcpS.
• Analysis of the Wzx-Wzy pathway.

Main Results:

• A novel protein, CcpS, was identified as a substrate for Stk1 phosphorylation.
• Phosphorylated CcpS modulates the activity of phosphatase CpsB.
• The crystal structure of CcpS revealed a phosphorylatable N-terminal region.
• CcpS links Stk1 to CPS synthesis by regulating CpsB activity and subsequent CpsD phosphorylation.

Conclusions:

• CcpS acts as a crucial link between STK signaling and CPS production in Streptococcus.
• CcpS phosphorylation by Stk1 inhibits CpsB phosphatase activity, impacting CPS synthesis.
• This finding provides a new molecular mechanism for regulating bacterial virulence factor production.