The oxazolidinone linezolid inhibits initiation of protein synthesis in bacteria

The oxazolidinones represent a new class of antimicrobial agents which are active against multidrug-resistant staphylococci, streptococci, and enteroc occi. Previous studies have demonstrated that oxazolidinones inhibit bacter ial translation in vitro at a step preceding elongation but after the charg ing of N-formylmethionine to the initiator tRNA molecule. The event that oc curs between these two steps is termed initiation. Initiation of protein sy nthesis requires the simultaneous presence of N-formylmethionine-tRNA, the 30S ribosomal subunit, mRNA, GTP, and the initiation factors IF1, IF2, and IF3, An initiation complex assay measuring the binding of [H-3]N-formylmeth ionyl-tRNA to ribosomes in response to mRNA binding was used in order to in vestigate the mechanism of oxazolidinone action. Linezolid inhibited initia tion complex formation with either the 30S or the 70S ribosomal subunits fr om Escherichia coli, In addition, complex formation with Staphylococcus aur eus 70S tight-couple ribosomes aas inhibited by linezolid, Linezolid did no t inhibit the independent binding of either mRNA or N-formylmethionyl-tRNA to E, coli 30S ribosomal subunits, nor did it prevent the formation of the IF2-N-formylmethionyl-tRNA binary complex. The results demonstrate that oxa zolidinones inhibit the formation of the initiation complex in bacterial tr anslation systems by preventing formation of the N-formylmethionyl-tRNA-rib osome-mRNA ternary complex.