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Polyamines affect diversely the antibiotic potency: insight gained from kinetic studies of the blasticidin S and spiramycin interactions with functional ribosomes

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http://pubman.mpdl.mpg.de/cone/persons/resource/persons50642

Wilson,  Daniel N.
Dept. of Vertebrate Genomics (Head: Hans Lehrach), Max Planck Institute for Molecular Genetics, Max Planck Society;

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Citation

Petropoulos, A. D., Xaplanteri, M. A., Dinos, G. P., Wilson, D. N., & Kalpaxis, D. L. (2004). Polyamines affect diversely the antibiotic potency: insight gained from kinetic studies of the blasticidin S and spiramycin interactions with functional ribosomes. Journal of Biological Chemistry, 279(25), 26518-26525. doi:10.1074/jbc.M313634200.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0010-8872-F
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 Ki), 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.