NEW ANTIBIOTIC THAT ACTS SPECIFICALLY ON THE GTP-BOUND FORM OF ELONGATION FACTOR-TU

The new thiazolyl peptide antibiotic GE2270 A, isolated from Planobispora rosea strain ATCC 53773, is shown to inhibit bacterial protein biosynthesis in vitro by affecting specifically the GTP-bound form of elongation factor Tu (EF-Tu). The 'off' rate of EF-Tu.GTP is slowed down 400-fold, locking GTP on EF-Tu, whereas EF-Tu.GDP is unaffected. Therefore, on the EF-Tu.guanine nucleotide interaction, GE2270 A mimics the effect of aa-tRNA. In line with this, the binding of aa-tRNA to EF-Tu.GTP is hindered by the antibiotic, as shown by the absence of a stable ternary complex and the inhibition of the enzymatic binding of aa-tRNA to the ribosome. This blocks the elongation cycle. GE2270 A does not essentially modify the intrinsic GTPase activity of EF-Tu, but impairs the stimulation by ribosomes of this reaction. The negative effect of GE2270 A on the EF-Tu.GTP interaction with aa-tRNA bears similarities with that of the structurally unrelated pulvomycin, whereas marked differences were found by comparing the effects of these two antibiotics on EF-Tu.GDP. This work emphasizes the varieties of the transitional conformations which tune the EF-Tu interaction with GTP and GDP.