Methicillin-resistant Staphylococcus aureus (MRSA) has acquired a unique penicillin- binding protein (PBP), PBP 2a, which has rendered the organism resistant to the action of all available β-lactam antibiotics. The X-ray structure of PBP 2a shows the active site in a closed conformation, consistent with resistance to inhibition by β-lactam antibiotics. However, it is known that PBP 2a avidly cross-links the S. aureus cell wall, which is its ...