The formation of functional penicillin-binding proteins

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Bacterial cell wall synthesis is a key target for antibiotics.
• Penicillin-binding proteins (PBPs) are essential enzymes in bacterial cell wall synthesis.
• Understanding antibiotic binding and inhibition mechanisms is vital for developing new antibacterial strategies.

Purpose of the Study:

• To develop a method for determining the binding capacity of [14C]benzylpenicillin and [14C]Cephapirin in Bacillus subtilis.
• To investigate the relationship between antibiotic binding, inhibition of functional protein synthesis, and bacterial cell density.
• To elucidate the role of cell-bound penicillinase in antibiotic resistance.

Main Methods:

• Development of a method to quantify [14C]benzylpenicillin and [14C]Cephapirin binding to Bacillus subtilis.
• Measurement of functional penicillin-binding protein formation under varying antibiotic concentrations.
• Assessment of total bacterial protein synthesis and D-alanine carboxypeptidase activity.

Main Results:

• [14C]benzylpenicillin inhibited functional PBPs but not total protein synthesis at plateau concentrations.
• Unbound penicillin in the medium, influenced by cell-bound penicillinase, is necessary for PBP inhibition.
• [14C]Cephapirin, resistant to penicillinase, effectively inhibited Cephapirin-binding proteins without affecting D-alanine carboxypeptidase.

Conclusions:

• Covalent binding of penicillin alone is insufficient to inhibit functional PBP formation; unbound antibiotic is required.
• Cell-bound penicillinase activity modulates unbound antibiotic concentration, affecting growth inhibition.
• Cephapirin's resistance to penicillinase allows for potent inhibition of its target PBPs, highlighting differential antibiotic mechanisms.