Farnesyl pyrophosphate (FPP) is utilized for many cellular processes, including the production of dolichols, ubiquinone (CoQ), sterols, farnesylated heme A and prenylated proteins. This lipid synthesized by FPP synthetase (ERG20) becomes attached to target proteins by the prenyltransferases, CDC43/RAM2 and RAM1/RAM2 complexes after the formation of the C15 and C20 units, respectively. Defects in protein prenylation as a result of inhibiting these enzyme complexes lead to pleiotropic effects in all eukaryotes. In this study, using Candida glabrata conditional mutants, the importance of the ERG20 and RAM2 genes for growth using both in vivo and in vitro assays was assessed by placing the RAM2 and ERG20 genes under the control of a regulatable promoter. Repression of RAM2 gene expression revealed growth defects under both conditions. However, repression of ERG20 gene expression did not impair fungal growth in a mouse host, but did result in growth defects on laboratory media. Thus, FPP synthase is not required for survival in an infected mouse, but the RAM2-encoded prenyltransferase was critical for growth under both conditions. This study strongly suggests that inhibitors of prenyltransferase may be promising antifungals.

Multidrug resistance in the pathogenic fungus Candida glabrata is a growing global threat. Here, we study mechanisms of multidrug resistance in this pathogen. Exposure of C. glabrata cells to micafungin (an echinocandin) leads to the isolation of a mutant exhibiting resistance to echinocandin and azole antifungals. The drug-resistant phenotype is due to a non-synonymous mutation (R70H) in gene IPI1, which is involved in pre-rRNA processing. Azole resistance in the ipi1^R70H mutant depends on the Pdr1 transcription factor, which regulates the expression of multidrug transporters. The C. glabrata Ipi1 protein physically interacts with the ribosome-related chaperones Ssb and Ssz1, both of which bind to Pdr1. The Ipi1-Ssb/Ssz1 complex inhibits Pdr1-mediated gene expression and multidrug resistance in C. glabrata, in contrast to Saccharomyces cerevisiae where Ssz1 acts as a positive regulator of Pdr1. Furthermore, micafungin exposure reduces metabolic activity and cell proliferation in the ipi1^R70H mutant, which may contribute to micafungin tolerance.