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Altered murein composition in a DD-carboxypeptidase mutant of Streptococcus pneumoniae
A Severin1, C Schuster, R Hakenbeck
1Rockefeller University, New York, New York 10021-6399.
Abstract:
The muropeptide composition of a Streptococcus pneumoniae mutant in which the DD-carboxypeptidase (penicillin-binding protein 3) gene was interrupted by plasmid insertion close to the 3' end of the gene was examined. Extensive compositional changes were observed: the linear pentapeptide, a minor component of the parental cells, became the most abundant monomeric peptide in the mutant wall, while the proportion of tripeptides that represent the main monomers in the parental cells was greatly reduced. The amount of the major dimer of parental cells, the directly cross-linked tri-tetrapeptide, was also reduced by a factor of 4. It was partially replaced by a novel dimer: the cross-linked product of a linear pentapeptide and a pentapeptide carrying a serylalanine dipeptide substituent on the epsilon-NH2 group of its lysine residue. This dimer together with two other dimeric peptides, each containing the serylalanine cross bridge, became the quantitatively major components of the mutant peptidoglycan.
Insights
Mutating Streptococcus pneumoniae penicillin-binding protein 3 significantly altered its muropeptide composition. The study reveals shifts in peptide monomers and dimers, impacting cell wall structure.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Streptococcus pneumoniae possesses a complex peptidoglycan cell wall essential for its structure and survival.
- Penicillin-binding proteins (PBPs) are crucial enzymes involved in bacterial cell wall synthesis and remodeling.
- PBP3, a DD-carboxypeptidase, plays a specific role in peptidoglycan cross-linking.
Purpose of the Study:
- To investigate the impact of PBP3 gene disruption on the muropeptide composition of Streptococcus pneumoniae.
- To identify changes in monomeric and dimeric peptide structures within the mutant cell wall.
Main Methods:
- Genetic manipulation of Streptococcus pneumoniae to create a PBP3 mutant by plasmid insertion.
- Detailed analysis of the muropeptide composition of both parental and mutant strains using chromatographic techniques.
Main Results:
- Disruption of the PBP3 gene led to extensive changes in muropeptide composition.
- The linear pentapeptide became the predominant monomer, while tripeptides decreased significantly.
- A novel dimer, formed by a linear pentapeptide and a substituted pentapeptide with a serylalanine bridge, emerged as a major component.
Conclusions:
- PBP3 is critical for the normal peptidoglycan structure of Streptococcus pneumoniae.
- The absence of functional PBP3 results in altered cross-linking pathways and the formation of novel peptidoglycan structures.