Increase of sensitivity to aminoglycoside antibiotics by polyamine-induced protein (oligopeptide-binding protein) in Escherichia coli.

The sensitivity of Escherichia coli to several aminoglycoside antibiotics was examined with E. coli DR112 transformed by the gene for polyamine-induced protein (oligopeptide-binding OppA] protein) or polyamine transport proteins. The results clearly showed that sensitivity to aminoglycoside antibiotics (gentamicin, isepamicin, kanamycin, neomycin, paromomycin, and streptomycin) increased due to the highly expressed OppA protein. When the gene for OppA protein was deleted, sensitivity to aminoglycoside antibiotics was greatly decreased. It was also shown that isepamicin could bind to OppA protein with a binding affinity constant of 8.5 x 10(3) M-1 under the ionic conditions of 50 mM K+ and 1 mM Mg2+ at pH 7.5, and isepamicin uptake into cells was greatly stimulated by the OppA protein. These results, taken together, show that the OppA protein increases the uptake of aminoglycoside antibiotics. In addition, the OppA protein increased the transport of spermidine and an oligopeptide (Gly-Leu-Tyr). The uptake of isepamicin into cells was partially inhibited by spermidine, suggesting that the binding site for isepamicin overlaps that for spermidine on the OppA protein. Spermidine uptake activity by the OppA protein was less than 1% of that of the ordinary spermidine uptake system. Aminoglycoside antibiotics neither stimulated the synthesis of OppA protein nor increased spermidine uptake.