By Meghan Bialt-DeCelie ‘19

The overuse of antibiotics is causing rapid increase in antibiotic resistant bacteria. Through a type IV secretion system, bacteria that aren’t killed by the antibiotics share their antibiotic resistant genes with other bacterial cells via bacterial conjugation. Researchers have been looking for a way to slow down the growing resistance. A study led by Dr. Bastien Casu from Université de Montréal found a new way to prevent the sharing of antibiotic resistant genes between bacteria by targeting the type IV secretion system.

Researchers looked for ways to block the active site of the TraE protein which is essential for the transfer of the pKM101 plasmid between bacterial cells. Using differential scanning fluorimetry (DSF), they first screened a small fragment library of 505 molecules to see if any of those molecules would bind to the target protein’s active site. This technique determines how stable a protein is in the presence of a particular ligand by increasing the temperature and monitoring the protein’s denaturation. From this library, they found 16 molecules that fit the criteria. The great majority of the molecules contained a carboxyl group which suggests that this group is involved in the interaction with the protein. Researchers used X-ray crystallography to get a better understanding of the structure of TraE and in silico docking to find fragments that could potentially bind to the protein’s binding site. They identified two fragments that could bind to TraE: 1E6 (2-furoic acid) and 4H10 (2-chloroisonicotinic acid).  They found that these fragments can fit in a known inhibitor binding site in a similarly structured protein VirB8-like.

Understanding the structure of a critical protein involved in bacterial conjugation can be useful in finding potential inhibitory molecules to slow the rapid increase in antibiotic resistance of disease-causing bacteria. For the future researchers can now test the effectiveness of these identified inhibitors on bacterial conjugation and finding the right combinations of these compounds.

References:

1. B. Casu, et. al., Fragment-based screening identifies novel targets for inhibitors of conjugative transfer of antimicrobial resistance by plasmid pKM101. Scientific Reports 7, (2017). doi:10.1038/s41598-017-14953-1.
2. Image retrieved from: https://commons.wikimedia.org/wiki/File:Antibiotic_sensitvity_and_resistance.jpg