Background: The need to develop new drugs to treat the growing problem of antibiotic resistance has been widely recognised.¹ One approach to do so is to identify compounds that inhibit bacterial virulence. The enzyme DsbA (a thiol-disulfide oxidoreductase) is a central regulator of bacterial virulence. DsbA is present in many Gram-negative bacteria and is essential for forming disulfide bonds between nascent polypeptide chains, thereby promoting the folding and stability of several proteins that are responsible for bacterial virulence.² Whilst knockout strains have been shown to be avirulent, there are currently no small molecule inhibitors of DsbA.

Results: Saturation transfer difference (STD) NMR spectroscopy was used as a first-pass screen of our in-house fragment library (1137 compounds, MW ~200 Da) against E. coli DsbA. From the STD-NMR screen 220 compounds were identified as potential binders of DsbA. Binding of these fragments was validated using heteronuclear multiple quantum coherence NMR spectra after which the overall hit-rate was 4%. Commercially available analogues of these hits were purchased to probe SAR. The structures of several protein-fragment complexes have been solved, which revealed that the fragments bind within a hydrophobic groove adjacent to the active site of DsbA.  The X-ray crystallography data across one particular series of fragments reveals a conserved binding location within the groove.

Conclusion: NMR screening results have been reported to predict the ligandability of a target. Ligandability is defined as the ability to identify compounds that both bind the target, and can be successfully developed into high affinity drug leads.³  Given that 4% of the fragments screened have been successfully identified as DsbA binders, and given that several share a conserved binding site within the hydrophobic groove of the protein, there is potential to further probe the SAR and develop the current fragments into high affinity lead-like compounds.