The StkP/PhpP Signaling Couple inStreptococcus pneumoniae: Cellular Organization and Physiological Characterization

Abstract

In Streptococcus pneumoniae, stkP and phpP, encoding the eukaryotic-type serine-threonine kinase and PP2C phosphatase, respectively, form an operon. PhpP has the features of a so-called "soluble" protein, whereas StkP protein is membrane associated. Here we provide the first genetic and physiological evidence that PhpP and StkP, with antagonist enzymatic activities, constitute a signaling couple. The StkP-PhpP couple signals competence upstream of the competence-specific histidine kinase ComD, receptor for the oligopeptide pheromone "competence stimulating peptide." We show that PhpP activity is essential in a stkP Signal transduction via the transfer of phosphoryl groups and transient protein phosphorylation involves the concerted activities of kinases and phosphatases and controls various cellular functions (for a review, see reference 18). In eubacteria, the histidine kinases of two-component systems (TCSs) and the phosphatases with which they interact are involved in cellular adaptation to environmental conditions (for a review, see reference 44). Serine-threonine kinases and PP2C phosphatases also contribute to regulatory and developmental processes, as described in Bacillus subtilis (1,2,13,23,29,33,43). In mycobacteria, a membrane-associated PP2C phosphatase controls the activity of several serine-threonine kinases (4, 6, 52), and the transcriptional activator EmbR has been identified as a phosphorylation target for PknH kinase (3, 4, 42). In Streptococcus agalactiae, the signaling pair Stk1-Stp1 plays a role in virulence, by modifying cytotoxin production and purine metabolism (34,35,36). In Streptococcus pyogenes, a histonelike protein is phosphorylated by the serine-threonine kinase, generating a substrate for the kinase-related phosphatase (21). The human pathogen Streptococcus pneumoniae has only one gene encoding a PP2C-type phosphatase, PhpP, located upstream from the stkP gene, which encodes the only membrane-associated serine-threonine kinase, StkP (17). The phpP and stkP genes overlap by 4 bp and form an operon (31). In a mouse model of infection, null mutations affecting StkP greatly attenuate tissue and bloodstream invasion (17). In cultures, these mutations are highly pleiotropic, presenting a notably important impact on competence development for genetic transformation (17, 40). In vitro studies have shown that autophosphorylated recombinant StkP (StkP-P) is a substrate for recombinant PhpP, suggesting that StkP and PhpP may function in a coordinated manner (31). However, the regulators controlling the cellular level of StkP-P and the network involving StkP in growing cultures remain ill defined. Recent studies of strain TIGR4 revealed that the transcriptional regulator RitR (45) is phosphorylated by StkP and dephosphorylated by PhpP (50). In order to get better insight into StkP signaling, we investigated the specific role of PhpP phosphatase on bacterial growth and on the development of competence for genetic transformation in cultures, by using genetic analysis. Specific null mutation in ...

Control of cell division in Streptococcus pneumoniae by the conserved Ser/Thr protein kinase StkP

“…S4). So far only StkP and RitR have been identified as targets of PhpP (26,27,38), but our analysis also identifies DivIVA as an in vivo target of PhpP.…”

“…Previous work has shown that StkP acts as a dimer (25) and forms a signaling couple with its cognate phosphatase PhpP, which is a predicted cytoplasmic protein (26,27). PASTA domains of StkP were shown to bind synthetic and native PG subunits and β-lactam antibiotics (28).…”

Eukaryote-Like Serine/Threonine Kinases and Phosphatases in Bacteria

“…The physiological functions of eSTPs are not as well understood as those of eSTKs, and Table 2 is a comprehensive list of their identified substrates. S. pyogenes eSTP and S. pneumoniae PhpP deletion mutants are nonviable, highlighting the importance of eSTPs in bacterial physiology (72,131). However, a deletion of S. pneumoniae PhpP could be obtained when the eSTK (StkP) located in the same operon was also deleted, suggesting that an important role of these phosphatases is to modulate the autophosphorylation state of their partner kinases (131).…”

“…S. pyogenes eSTP and S. pneumoniae PhpP deletion mutants are nonviable, highlighting the importance of eSTPs in bacterial physiology (72,131). However, a deletion of S. pneumoniae PhpP could be obtained when the eSTK (StkP) located in the same operon was also deleted, suggesting that an important role of these phosphatases is to modulate the autophosphorylation state of their partner kinases (131). For example, autophosphorylated StkP is a substrate for PhpP (125), the kinase activity of autophosphorylated M. tuberculosis PknB is reduced by PstP-mediated dephosphorylation (18,26), B. subtilis PrpC dephosphorylates PrkC in vitro (127), the enzymatic function of the Bacillus anthracis eSTK Ba-Stk1 is reduced after desphosphorylation by the eSTP Ba-Stp1 (161), and a strong interaction was reported between the M. xanthus eSTP Pph1 and the eSTK Pkn5 (180).…”

Serine/Threonine Phosphatase Stp1 Mediates Post-transcriptional Regulation of Hemolysin, Autolysis, and Virulence of Group B Streptococcus

“…Streptococcus sp.) also led to the notion that it may be essential (9,10,26). Recently, Agarwal et al (27) described the importance of the Stp1 homologue (SP-STP) of Group A Streptococcus (GAS) to its pathogenesis.…”