Abstract
Biosynthesis of glycosylphosphatidylinositol (GPI) is required for anchoring proteins to the plasma membrane, and is essential for the integrity of the fungal cell wall. Here, we use a reporter gene-based screen in Saccharomyces cerevisiae for the discovery of antifungal inhibitors of GPI-anchoring of proteins, and identify the oligocyclopropyl-containing natural product jawsamycin (FR-900848) as a potent hit. The compound targets the catalytic subunit Spt14 (also referred to as Gpi3) of the fungal UDP-glycosyltransferase, the first step in GPI biosynthesis, with good selectivity over the human functional homolog PIG-A. Jawsamycin displays antifungal activity in vitro against several pathogenic fungi including Mucorales, and in vivo in a mouse model of invasive pulmonary mucormycosis due to Rhyzopus delemar infection. Our results provide a starting point for the development of Spt14 inhibitors for treatment of invasive fungal infections.
Highlights
Biosynthesis of glycosylphosphatidylinositol (GPI) is required for anchoring proteins to the plasma membrane, and is essential for the integrity of the fungal cell wall
Using phenotypic screens and chemical genetics, a set of synthetic compounds have been identified as inhibitors of Gwt[15,9], a protein involved in the acylation of inositol early in the GPI pathway, and a natural product chemotype as an inhibitor of Mcd[410,11], an ethanolamine phosphotransferase later in the process
To identify novel inhibitors of the GPI pathway, we adapted a previously published reporter construct expressing the small Gaussia princeps luciferase gene fused to the GPI-anchoring signal of Candida albicans PGA5918 (Fig. 1a)
Summary
Biosynthesis of glycosylphosphatidylinositol (GPI) is required for anchoring proteins to the plasma membrane, and is essential for the integrity of the fungal cell wall. Despite increasing numbers of affected patients with lifethreatening infections and the concomitant increased burden on public healthcare systems, there remains only three main classes of established antifungal agents to treat systemic infections These are the polyenes, azoles, and echinocandins which act on the fungal plasma membrane, its biosynthesis pathway or cell wall components, respectively[3]. Using phenotypic screens and chemical genetics, a set of synthetic compounds have been identified as inhibitors of Gwt[15,9], a protein involved in the acylation of inositol early in the GPI pathway, and a natural product chemotype as an inhibitor of Mcd[410,11], an ethanolamine phosphotransferase later in the process (all reviewed in detail by Mutz and Roemer[12]) Despite this limited chemical armamentarium, the combined experimental data collected using these compounds strongly supports the GPI pathway as an attractive starting point for novel antifungal therapies.
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