Antibiotics MDL 62,879 and kirromycin bind to distinct and independent sites of elongation factor Tu (EF-Tu).
Antibiotic MDL 62,879 inhibits bacterial protein synthesis by acting on elongation factor Tu (EF-Tu). In this study we show that the inhibition of protein synthesis by MDL 62,879 in an Escherichia coli cell-free system was fully reversed by addition of stoichiometric amounts of EF-Tu but not by large excesses of EF-Ts, ribosomes, or aa-tRNA. MDL 62,879 bound tightly to EF-Tu and formed a stable 1:1 MDL 62,879:EF-Tu (M:EF-Tu) complex. We show that binding of MDL 62,879 to EF-Tu strongly affects the interaction of EF-Tu with aa-tRNA and causes rapid dissociation of preformed EF-Tu.aa-tRNA complex, suggesting that inhibition of aa-tRNA binding is due to a conformational change in EF-Tu rather than competition for the aa-tRNA binding site. Indication of a conformational change in EF-Tu induced by MDL 62,879 is further confirmed by proteolytic cleavage experiments: MDL 62,879 binding strongly protects EF-Tu against trypsin cleavage. The observed effects of MDL 62,879 appear to be different from those of the kirromycin class of antibiotics, which also inhibit protein synthesis by binding to EF-Tu, suggesting two distinct binding sites. Indeed, the M:EF-Tu complex was able to bind stoichiometric amounts of kirromycin to form a 1:1:1 M:EF-Tu:kirromycin (M:EF-Tu:K) complex, providing direct evidence that the two antibiotics bind to independent and distinct sites on the EF-Tu molecule. The interaction of the M:EF-Tu:K complex with aa-tRNA and other co-factors suggest that the contemporary binding of the two antibiotics locks EF-Tu into an intermediate conformation in which neither antibiotic exhibits complete dominance.
Landini
P
P
Lepetit Research Center, Gerenzano (Varese), Italy.
Soffientini
A
A
Monti
F
F
Lociuro
S
S
Marzorati
E
E
Islam
K
K
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000378:metabolism*; D001665:Binding Sites; D002851:Chromatography, High Pressure Liquid; D008956:Models, Chemical; D010444:Peptide Elongation Factor Tu / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D010456:Peptides, Cyclic / Q000378:metabolism*; D011072:Poly U / Q000378:metabolism; D011728:Pyridones / Q000378:metabolism; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D013844:Thiazoles / Q000378:metabolism
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D010455:Peptides; D010456:Peptides, Cyclic; D011728:Pyridones; D012346:RNA, Transfer, Amino Acyl; D013844:Thiazoles; C012521:pulvomycin; D011072:Poly U; C012001:polyphenylalanine; D010444:Peptide Elongation Factor Tu; C068122:GE 2270 A; C008536:mocimycin