Vancomycin acts by binding to which target in bacterial cell wall synthesis, distinguishing it from beta-lactams?
- A Penicillin-binding proteins (PBPs) at the transpeptidase active site
- B The MurA enzyme that initiates peptidoglycan synthesis
- C The D-Ala-D-Ala terminus of the NAM-pentapeptide precursor, sterically blocking both transglycosylation and transpeptidation ✓
- D The beta-lactam binding site on transpeptidases
Correct answer: C. The D-Ala-D-Ala terminus of the NAM-pentapeptide precursor, sterically blocking both transglycosylation and transpeptidation
Explanation
Vancomycin is a glycopeptide that forms hydrogen bonds with the D-Ala-D-Ala terminal residues of the lipid II peptidoglycan precursor, physically blocking both transglycosylase (polymerization) and transpeptidase (cross-linking) reactions. It does not bind PBPs. Vancomycin-resistant enterococci (VRE) modify the terminal D-Ala-D-Ala to D-Ala-D-Lac (vanA, vanB genes), reducing binding affinity ~1000-fold. Beta-lactams bind PBPs; bacitracin inhibits lipid carrier recycling; fosfomycin inhibits MurA.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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