# Substitution of Glu378 in EF-Tu disrupts binding to KKL-55

## TL;DR

Researchers found that changing a specific amino acid in EF-Tu disrupts its binding to an antibiotic candidate, KKL-55, and reduces protein translation.

## Contribution

The study shows that a tryptophan substitution at position 378 of EF-Tu significantly weakens KKL-55 binding and inhibits translation.

## Key findings

- EF-Tu variant with tryptophan at position 378 increases KKL-55 binding Kd by over 6-fold.
- The E378W variant reduces in vitro translation and blocks trans-translation.
- Residue 378 is part of the KKL-55 binding pocket in EF-Tu.

## Abstract

Trans
-translation is a target for the development of new antibiotics. The potential antibiotic lead compound KKL-55 binds to EF-Tu and inhibits
trans
-translation. Previous structural and biochemical studies showed that glutamate 378 in EF-Tu directly contacts bound KKL-55, but mutation of residue 378 to alanine had no effect on the equilibrium dissociation constant for binding of EF-Tu and KKL-55. Here, we found that a variant of EF-Tu with tryptophan at position 378 increases the

K
d

for binding of EF-Tu and KKL-55 by >6-fold, indicating that a larger side chain at this position is disruptive. The E378W variant decreased the amount of translation
in vitro
and no
trans
-translation could be detected with this variant. These data provide further evidence that residue 378 of EF-Tu forms part of the KKL-55 binding pocket and are consistent with a lack of spontaneous mutants resistant to KKL-55.