Structural basis for full-spectrum inhibition of translational functions on a tRNA synthetase

The polyketide natural product borrelidin displays Antibacterial, Antifungal, antimalarial, Anticancer, insecticidal and herbicidal activities through the selective inhibition of threonyl-tRNA synthetase (ThrRS). How borrelidin simultaneously attenuates Bacterial growth and suppresses a variety of infections in Plants and Animals is not known. Here we show, using X-ray crystal structures and functional analyses, that a single molecule of borrelidin simultaneously occupies four distinct subsites within the catalytic domain of Bacterial and human ThrRSs. These include the three substrate-binding sites for amino acid, ATP and tRNA associated with aminoacylation, and a fourth 'orthogonal' subsite created as a consequence of binding. Thus, borrelidin competes with all three aminoacylation substrates, providing a potent and redundant mechanism to inhibit ThrRS during protein synthesis. These results highlight a surprising natural design to achieve the quadrivalent inhibition of translation through a highly conserved family of enzymes.