Aspergillus fumigatus may present a spectrum of clinical, diagnostic and therapeutic challenges. A new generation of antifungal agents is required to address the toxicity and emerging reports of resistance in existing therapies. The cell wall of A. fumigatus (Af) is essential for survival of the fungus and represents a drug target. Chitin, an integral component, consists of linear β(1-4) linked N-acetyl-D-glucosamine (GlcNAc). A new potential antifungal target is glucosamine-6-phosphate N-acetyltransferase (AfGNA1). This enzyme N-acetylates glucosamine-6-phosphate to N-acetyl-glucosamine-6-phosphate as an intermediary step in UDP-GlcNAc biosynthesis. Fragment-based drug discovery provides a complementary and contrasting approach to traditional high-throughput methods by elaborating weakly binding small molecules. Here we assess the druggability of biotinylated AfGNA1 using a fragment screen based on bio-layer interferometry (Octet Red, Forte Bio). Screening the Dundee Drug Discovery Unit (DDU) fragment library gave a preliminary hit rate of 5.7% (37/652 with a response rate > 0.02 nm). A subset of seven fragments demonstrated stoichiometric binding with equilibrium dissociation constants in the micromolar range. Structural analysis of AfGNA1 in complex with fragment (A) illustrated the fragment binds in a groove behind the sugar substrate. Initial kinetic data suggested partial enzyme inhibition. This work suggests AfGNA1 may be a druggable antifungal target.
Full conference title:
- MS 2013