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LytF, a novel competence-regulated murein hydrolase in the genus Streptococcus.

ABSTRACT: Streptococcus pneumoniae and probably most other members of the genus Streptococcus are competent for natural genetic transformation. During the competent state, S. pneumoniae produces a murein hydrolase, CbpD, that kills and lyses noncompetent pneumococci and closely related species. Previous studies have shown that CbpD is essential for efficient transfer of genomic DNA from noncompetent to competent cells in vitro. Consequently, it has been proposed that CbpD together with the cognate immunity protein ComM constitutes a DNA acquisition mechanism that enables competent pneumococci to capture homologous DNA from closely related streptococci sharing the same habitat. Although genes encoding CbpD homologs or CbpD-related proteins are present in many different streptococcal species, the genomes of a number of streptococci do not encode CbpD-type proteins. In the present study we show that the genomes of nearly all species lacking CbpD encode an unrelated competence-regulated murein hydrolase termed LytF. Using Streptococcus gordonii as a model system, we obtained evidence indicating that LytF is a functional analogue of CbpD. In sum, our results show that a murein hydrolase gene is part of the competence regulon of most or all streptococcal species, demonstrating that these muralytic enzymes constitute an essential part of the streptococcal natural transformation system.

SUBMITTER: Berg KH

PROVIDER: S-EPMC3264080 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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LytF, a novel competence-regulated murein hydrolase in the genus Streptococcus.

Berg Kari Helene KH Ohnstad Hilde Solheim HS Håvarstein Leiv Sigve LS

Journal of bacteriology 20111128 3

Streptococcus pneumoniae and probably most other members of the genus Streptococcus are competent for natural genetic transformation. During the competent state, S. pneumoniae produces a murein hydrolase, CbpD, that kills and lyses noncompetent pneumococci and closely related species. Previous studies have shown that CbpD is essential for efficient transfer of genomic DNA from noncompetent to competent cells in vitro. Consequently, it has been proposed that CbpD together with the cognate immunit ...[more]

PMID: 22123253

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Project description:The overall health of the oral cavity is dependent on proper homeostasis between health-associated bacterial colonizers and bacteria known to promote dental caries. Streptococcus sanguinis is a health-associated commensal organism, a known early colonizer of the acquired tooth pellicle, and is naturally competent. We have shown that LytF, a competence-controlled murein hydrolase, is capable of inducing the release of extracellular DNA (eDNA) from oral bacteria. Precipitated LytF and purified LytF were used as treatments against planktonic cultures and biofilms. Larger amounts of eDNA were released from cultures treated with protein samples containing LytF. Additionally, LytF could affect biofilm formation and cellular morphology. Biofilm formation was significantly decreased in the lytF-complemented strain, in which increased amounts of LytF are present. The same strain also exhibited cell morphology defects in both planktonic cultures and biofilms. Furthermore, the LytF cell morphology phenotype was reproducible in wild-type cells using purified LytF protein. In sum, our findings demonstrate that LytF can induce the release of eDNA from oral bacteria, and they suggest that, without proper regulation of LytF, cells display morphological abnormalities that contribute to biofilm malformation. In the context of the oral biofilm, LytF may play important roles as part of the competence and biofilm development programs, as well as increasing the availability of eDNA.IMPORTANCEStreptococcus sanguinis, a commensal organism in the oral cavity and one of the pioneer colonizers of the tooth surface, is associated with the overall health of the oral environment. Our laboratory showed previously that, under aerobic conditions, S. sanguinis can produce H2O2 to inhibit the growth of bacterial species that promote dental caries. This production of H2O2 by S. sanguinis also induces the release of eDNA, which is essential for proper biofilm formation. Under anaerobic conditions, S. sanguinis does not produce H2O2 but DNA is still released. Determining how S. sanguinis releases DNA is thus essential to understand biofilm formation in the oral cavity.

Project description:UnlabelledCompetence for genetic transformation in Streptococcus pneumoniae develops in response to accumulation of a secreted peptide pheromone and was one of the initial examples of bacterial quorum sensing. Activation of this signaling system induces not only expression of the proteins required for transformation but also the production of cellular chaperones and proteases. We have shown here that activity of this pathway is sensitively responsive to changes in the accuracy of protein synthesis that are triggered by either mutations in ribosomal proteins or exposure to antibiotics. Increasing the error rate during ribosomal decoding promoted competence, while reducing the error rate below the baseline level repressed the development of both spontaneous and antibiotic-induced competence. This pattern of regulation was promoted by the bacterial HtrA serine protease. Analysis of strains with the htrA (S234A) catalytic site mutation showed that the proteolytic activity of HtrA selectively repressed competence when translational fidelity was high but not when accuracy was low. These findings redefine the pneumococcal competence pathway as a response to errors during protein synthesis. This response has the capacity to address the immediate challenge of misfolded proteins through production of chaperones and proteases and may also be able to address, through genetic exchange, upstream coding errors that cause intrinsic protein folding defects. The competence pathway may thereby represent a strategy for dealing with lesions that impair proper protein coding and for maintaining the coding integrity of the genome.ImportanceThe signaling pathway that governs competence in the human respiratory tract pathogen Streptococcus pneumoniae regulates both genetic transformation and the production of cellular chaperones and proteases. The current study shows that this pathway is sensitively controlled in response to changes in the accuracy of protein synthesis. Increasing the error rate during ribosomal decoding induced competence, while decreasing the error rate repressed competence. This pattern of regulation was promoted by the HtrA protease, which selectively repressed competence when translational fidelity was high but not when accuracy was low. Our findings demonstrate that this organism is able to monitor the accuracy of information used for protein biosynthesis and suggest that errors trigger a response addressing both the immediate challenge of misfolded proteins and, through genetic exchange, upstream coding errors that may underlie protein folding defects. This pathway may represent an evolutionary strategy for maintaining the coding integrity of the genome.

Project description:LyrA (SpdC), a homologue of eukaryotic CAAX proteases that act on prenylated substrates, has been implicated in the assembly of several pathways of the envelope of Staphylococcus aureus. We described earlier the Lysostaphin resistance (Lyr) and Staphylococcal protein A display (Spd) phenotypes associated with loss of the lyrA (spdC) gene. However, a direct contribution to the assembly of pentaglycine crossbridges, the target of lysostaphin cleavage in S. aureus peptidoglycan, or of Staphylococcal protein A attachment to peptidoglycan could not be attributed directly to LyrA (SpdC). These two processes are catalyzed by the Fem factors and Sortase A, respectively. To gain insight into the function of LyrA (SpdC), here we use affinity chromatography and LC-MS/MS analysis and report that LyrA interacts with SagB. SagB cleaves glycan strands of peptidoglycan to achieve physiological length. Similar to sagB peptidoglycan, lyrA peptidoglycan contains extended glycan strands. Purified lyrA peptidoglycan can still be cleaved to physiological length by SagB in vitro LyrA does not modify or cleave peptidoglycan, it also does not modify or stabilize SagB. The membrane bound domain of LyrA is sufficient to support SagB activity but predicted 'CAAX enzyme' catalytic residues in this domain are dispensable. We speculate that LyrA exerts its effect on bacterial prenyl substrates, specifically undecaprenol-bound peptidoglycan substrates of SagB, to help control glycan length. Such an activity also explains the Lyr and Spd phenotypes observed earlier.IMPORTANCE Peptidoglycan is assembled on the trans side of the plasma membrane from lipid II precursors into glycan chains that are crosslinked at stem peptides. In S. aureus, SagB, a membrane-associated N-acetylglucosaminidase, cleaves polymerized glycan chains to their physiological length. Deletion of sagB is associated with longer glycan strands in peptidoglycan, altered protein trafficking and secretion in the envelope, and aberrant excretion of cytosolic proteins. It is not clear whether SagB, with its single transmembrane segment, serves as the molecular ruler of glycan chains or whether other factors modulate its activity. Here, we show that LyrA (SpdC), a protein of the CAAX type II prenyl endopeptidase family, modulates SagB activity via interaction though its transmembrane domain.

Project description:BackgroundSigX (σX), the alternative sigma factor of Streptococcus mutans, is the key regulator for transcriptional activation of late competence genes essential for taking up exogenous DNA. Recent studies reveal that adaptor protein MecA and the protease ClpC act as negative regulators of competence by a mechanism that involves MecA-mediated proteolysis of SigX by the ClpC in S. mutans. However, the molecular detail how MecA and ClpC negatively regulate competence in this species remains to be determined. Here, we provide evidence that adaptor protein MecA targets SigX for degradation by the protease complex ClpC/ClpP when S. mutans is grown in a complex medium.ResultsBy analyzing the cellular levels of SigX, we demonstrate that the synthesis of SigX is transiently induced by competence-stimulating peptide (CSP), but the SigX is rapidly degraded during the escape from competence. A deletion of MecA, ClpC or ClpP results in the cellular accumulation of SigX and a prolonged competence state, while an overexpression of MecA enhances proteolysis of SigX and accelerates the escape from competence. In vitro protein-protein interaction assays confirm that MecA interacts with SigX via its N-terminal domain (NTD1-82) and with ClpC via its C-terminal domain (CTD123-240). Such an interaction mediates the formation of a ternary SigX-MecA-ClpC complex, triggering the ATP-dependent degradation of SigX in the presence of ClpP. A deletion of the N-terminal or C-terminal domain of MecA abolishes its binding to SigX or ClpC. We have also found that MecA-regulated proteolysis of SigX appears to be ineffective when S. mutans is grown in a chemically defined medium (CDM), suggesting the possibility that an unknown mechanism may be involved in negative regulation of MecA-mediated proteolysis of SigX under this condition.ConclusionAdaptor protein MecA in S. mutans plays a crucial role in recognizing and targeting SigX for degradation by the protease ClpC/ClpP. Thus, MecA actually acts as an anti-sigma factor to regulate the stability of SigX during competence development.

Dataset Information

LytF, a novel competence-regulated murein hydrolase in the genus Streptococcus.

Publications

LytF, a novel competence-regulated murein hydrolase in the genus Streptococcus.

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