PMID:15075341

Citation	Petropoulos, AD, Xaplanteri, MA, Dinos, GP, Wilson, DN and Kalpaxis, DL (2004) Polyamines affect diversely the antibiotic potency: insight gained from kinetic studies of the blasticidin S AND spiramycin interactions with functional ribosomes. J. Biol. Chem. 279:26518-25
Abstract	The effects of spermine on peptidyltransferase inhibition by an aminohexosylcytosine nucleoside, blasticidin S, and by a macrolide, spiramycin, were investigated in a model system derived from Escherichia coli, in which a peptide bond is formed between puromycin and AcPhe-tRNA bound at the P-site of poly(U)-programmed ribosomes. Kinetics revealed that blasticidin S, after a transient phase of interference with the A-site, is slowly accommodated near to the P-site so that peptide bond is still formed but with a lower catalytic rate constant. At high concentrations of blasticidin S (>10 x K(i)), a second drug molecule binds to a weaker binding site on ribosomes, and this may account for the onset of a subsequent mixed-noncompetitive inhibition phase. Spermine enhances the blasticidin S inhibitory effect by facilitating the drug accommodation to both sites. On the other hand, spiramycin (A) was found competing with puromycin for the A-site of AcPhe-tRNA.poly(U).70 S ribosomal complex (C) via a two-step mechanism, according to which the fast formation of the encounter complex CA is followed by a slow isomerization to a tighter complex, termed C(*)A. In contrast to that observed with blasticidin S, spermine reduced spiramycin potency by decreasing the formation and stability of complex C(*)A. Polyamine effects on drug binding were more pronounced when a mixture of spermine and spermidine was used, instead of spermine alone. Our kinetic results correlate well with cross-linking and crystallographic data and suggest that polyamines bound at the vicinity of the antibiotic binding pockets modulate diversely the interaction of these drugs with ribosomes.
Links	PubMed Online version:10.1074/jbc.M313634200
Keywords	Anti-Bacterial Agents/pharmacology; Base Sequence; Binding Sites; Binding, Competitive; Escherichia coli/metabolism; Kinetics; Models, Biological; Models, Chemical; Models, Molecular; Molecular Sequence Data; Nucleosides/chemistry; Peptides/chemistry; Polyamines/chemistry; Protein Binding; Protein Structure, Secondary; Puromycin/chemistry; RNA, Ribosomal, 23S/chemistry; Ribosomes/metabolism; Spiramycin/chemistry; Time Factors
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