Untangling topoisomerase inhibition by protein toxins through cryo-electron microscopy and crystallography

Mycobacterium tuberculosis (Mtb) infects one-third of the world's population and in 2015 accounted for 1.8 million deaths, overtaking HIV as the most deadly human pathogen. We have recently demonstrated how clinically-utilised fluoroquinolone antibiotics (global sales ~$8 bn) inhibit DNA gyrase from Mtb, an essential topoisomerase necessary for DNA replication and maintenance of DNA supercoiling. This work also highlighted how antibiotic resistance is rendering fluoroquinolones ineffective. There is an abundance of alternative naturally-occurring antibiotics, from toxin-antitoxin systems, that can target DNA gyrase. Mtb encodes at least eighty different toxin-antitoxin loci, which perform multiple roles such as protection from antibiotics and controlling dormancy inside host macrophages, by specifically halting cell growth. These loci include homologues of the parDE family, which inhibit DNA gyrase. We propose to study the biochemical and structural basis of DNA gyrase inhibition by ParE toxins. Studying these complexes will generate new ways to inhibit a proven therapeutic target using toxins validated by millennia of bacterial evolution.