Peptidoglycan Cross-Linking Preferences of Staphylococcus aureus Penicillin-Binding Proteins Have Implications for...

Area of Science:

• Microbiology
• Drug Discovery
• Biochemistry

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant global health threat.
• MRSA's resistance to beta-lactam antibiotics is mediated by the acquisition of PBP2a.
• A hypothesis suggests PBP2a's substrate specificity differs from native S. aureus PBPs, impacting its function.

Purpose of the Study:

• To experimentally test the substrate specificity of PBP2a compared to native S. aureus transpeptidases.
• To investigate the role of glycine branch length in peptidoglycan cross-linking by PBP2a.
• To identify potential new targets for restoring beta-lactam sensitivity in MRSA.

Main Methods:

• Purified PBP2a and native S. aureus transpeptidases were used in vitro.
• Peptidoglycan strands with varying glycine branch lengths (penta-, tri-, and monoglycine) were synthesized and utilized as substrates.
• Experiments were conducted using both purified enzymes and whole bacterial cells.

Main Results:

• Purified PBP2a successfully cross-linked peptidoglycan strands with penta- and triglycine branches.
• PBP2a demonstrated an inability to cross-link peptidoglycan strands with monoglycine branches.
• In-cell experiments corroborated the in vitro findings regarding PBP2a's substrate preference.

Conclusions:

• PBP2a's inability to process monoglycine-containing peptidoglycan suggests a critical difference in its enzymatic activity compared to native enzymes.
• The enzyme FemA, responsible for extending monoglycine to triglycine, is implicated as a promising therapeutic target.
• Targeting FemA could lead to the development of novel small molecules to re-sensitize MRSA to beta-lactam antibiotics.