Inhibition of the ribosomal peptidyl transferase reaction by the mycarose moiety of the antibiotics carbomycin, spiramycin and tylosin

Many antibiotics, including the macrolides, inhibit protein synthesis by bi nding to ribosomes. Only some of the macrolides affect the peptidyl transfe rase reaction. The 16-member ring macrolide antibiotics carbomycin, spiramy cin, and tylosin inhibit peptidyl transferase. All these have a disaccharid e at position 5 in the lactone ring with a mycarose moiety. We have investi gated the functional role of this mycarose moiety. The 14-member ring macro lide erythromycin and the 16-member ring macrolides desmycosin and chalcomy cin do not inhibit the peptidyl transferase reaction. These drugs have a mo nosaccharide at position 5 in the lactone ring. The presence of mycarose wa s correlated with inhibition of peptidyl transferase, footprints on 23 S rR NA and whether the macrolide can compete with binding of hygromycin A to th e ribosome. The binding sites of the macrolides to Escherichia coli ribosom es were investigated by chemical probing of domains II and V of 23 S rRNA. The common binding site is around position A2058, while effects on U2506 de pend on the presence of the mycarose sugar. Also, protection at position A7 52 indicates that a mycinose moiety at position 14 in 16-member ring macrol ides interact with hairpin 35 in domain II. Competitive footprinting of rib osomal binding of hygromycin A and macrolides showed that tylosin and spira mycin reduce the hlrgromycin A protections of nucleotides in 23 S rRNA and that carbomycin abolishes its binding. In contrast, the macrolides that do not inhibit the peptidyl transferase reaction bind to the ribosomes concurr ently with hygromycin A. Data are presented to argue that a disaccharide at position 5 in the lactone ring of macrolides is essential for inhibition o f peptide bond formation and that the mycarose moiety is placed near the co nserved U2506 in the central loop region of domain V 23 S rRNA. (C) 2000 Ac ademic Press.