Aspergillus fumigatus is the most common mould causing infection worldwide in immunocompromised patients. Because of the increased number of infections caused by this filamentous fungi and the inefficacy of the available drugs, there is an urgent need for better drugs. The fungal cell wall is essential for the viability of Aspergillus fumigatus and is composed mainly of a fibrillar branched β 1,3-glucan core bound to chitin, galactomannan and β 1,3-1,4-glucan, embedded in an amorphous cement composed of α 1,3-glucan, galactomannan and polygalactosamine. Chitin is a 1,4 β linked polymer of N-acetyl-D-glucosamine (GlcNAc) synthesised by chitin synthase and it is essential for cell viability and mother-daughter cell separation. Thus, the synthesis of UDP-GlcNAc, which is the substrate of chitin synthase, is also essential. Four different enzymes carry out the biosynthesis of UDP-GlcNAc. We describe the crystal structures of two of them: the Aspergillus fumigatus glucosamine-6-phosphate Nacetyltransferase (AfGNA1), in complex with glucose-6P, and the phosphorylated form of GlcNAc-phosphomutase (AfAGM1), in complex with GlcNAc-6P and magnesium. In addition we also show the native human GNA1 crystal structure in complex with GlcNAc-6P and CoA, in order to compare the active sites. Inferred by mutagenesis studies and the different environment around the sugar compared to the human crystal structure, we suggest AfGNA1 as an attractive drug target. We also discuss the catalytic mechanism based on kinetic and structural studies of Tyr174Phe from AfGNA1. With regard to the AfAGM1 crystal structure, we discuss the trapping of a catalytic intermediate.
Full conference title:
The First International Fungal / Plant Cell Wall Meeting
- International Fungal / Plant Cell Wall Meeting 1st