Linezolid is active against VRE and MRSA by a mechanism distinct from all other protein synthesis inhibitors. Which of the following correctly describes its mechanism?
- A Binds 30S ribosomal subunit, inhibiting translocation
- B Binds 23S rRNA of the 50S subunit, preventing formation of the 70S initiation complex ✓
- C Binds 50S subunit at the peptidyl transferase centre, preventing translocation
- D Inhibits isoleucyl-tRNA synthetase, preventing aminoacyl-tRNA charging
Correct answer: B. Binds 23S rRNA of the 50S subunit, preventing formation of the 70S initiation complex
Explanation
Linezolid (an oxazolidinone) uniquely binds to the 23S rRNA component of the 50S ribosomal subunit, blocking formation of the 70S initiation complex — a step upstream of other ribosomal antibiotics. This novel binding site explains the lack of cross-resistance with macrolides, chloramphenicol, or aminoglycosides. Chloramphenicol and macrolides inhibit peptidyl transferase/translocation, aminoglycosides bind 30S and cause misreading, and mupirocin targets isoleucyl-tRNA synthetase.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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