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Peptidoglycan composition of a highly methicillin-resistant Staphylococcus aureus strain. The role of penicillin
B L de Jonge1, Y S Chang, D Gage
1Laboratory of Microbiology, Rockefeller University, New York, New York 10021.
Abstract:
All clinical isolates of methicillin-resistant Staphylococcus aureus contain an extra penicillin binding protein (PBP) 2A in addition to four PBPs present in all staphylococcal strains. This extra PBP is thought to be a transpeptidase essential for the continued cell wall synthesis and growth in the presence of beta-lactam antibiotics. As an approach of testing this hypothesis we compared the muropeptide composition of cell walls of a highly methicillin-resistant S. aureus strain containing PBP2A and its isogenic Tn551 derivative with reduced methicillin resistance, which contained no PBP2A because of the insertional inactivation of the PBP2A gene. Purified cell walls were hydrolyzed into muropeptides which were subsequently resolved by reversed-phase high-performance liquid chromatography and identified by chemical and mass spectrometric analysis. The peptidoglycan composition of the two strains were identical. Both peptidoglycans were highly cross-linked mainly through pentaglycine cross-bridges, although other, chemically distinct peptide cross-bridges were also present including mono-, tri-, and tetraglycine; alanine; and alanyl-tetraglycine. Our experiments provided no experimental data for a unique transpeptidase activity associated with PBP2A.
Insights
Penicillin-binding protein 2A (PBP2A) in methicillin-resistant Staphylococcus aureus (MRSA) was investigated. Muropeptide analysis revealed identical peptidoglycan composition between MRSA strains with and without PBP2A, challenging its unique transpeptidase role.
Area of Science:
- Microbiology
- Biochemistry
- Molecular Biology
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) possesses penicillin-binding protein 2A (PBP2A), an additional protein thought to be crucial for beta-lactam resistance.
- PBP2A is hypothesized to function as a transpeptidase, essential for cell wall synthesis in the presence of beta-lactam antibiotics.
Purpose of the Study:
- To investigate the role of PBP2A in MRSA cell wall synthesis.
- To test the hypothesis that PBP2A possesses unique transpeptidase activity essential for MRSA resistance.
Main Methods:
- Comparative analysis of muropeptide composition in MRSA strains with and without PBP2A.
- Hydrolysis of purified cell walls into muropeptides.
- Resolution of muropeptides using reversed-phase high-performance liquid chromatography (RP-HPLC).
- Identification of muropeptides via chemical and mass spectrometric analysis.
Main Results:
- The peptidoglycan composition of the PBP2A-containing MRSA strain and its isogenic derivative lacking PBP2A were identical.
- Both strains exhibited highly cross-linked peptidoglycans, primarily through pentaglycine cross-bridges.
- Other peptide cross-bridges, including mono-, tri-, and tetraglycine, alanine, and alanyl-tetraglycine, were also identified.
Conclusions:
- The study found no experimental evidence supporting a unique transpeptidase activity for PBP2A.
- The identical peptidoglycan composition suggests that PBP2A may not be solely responsible for essential transpeptidase functions in MRSA cell wall synthesis.
- Further research is needed to fully elucidate the specific role of PBP2A in MRSA beta-lactam resistance.