Identification of cyclosporin C from Amphichorda felina using a Cryptococcus neoformans differential temperature sensitivity assay.
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2018-03
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We used a temperature differential assay with the opportunistic fungal pathogen Cryptococcus neoformans as a simple screening platform to detect small molecules with antifungal activity in natural product extracts. By screening of a collection extracts from two different strains of the coprophilous fungus, Amphichorda felina, we detected strong, temperature-dependent antifungal activity using a two-plate agar zone of inhibition assay at 25 and 37 °C. Bioassay-guided fractionation of the crude extract followed by liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance spectroscopy (NMR) identified cyclosporin C (CsC) as the main component of the crude extract responsible for growth inhibition of C. neoformans at 37 °C. The presence of CsC was confirmed by comparison with a commercial standard. We sequenced the genome of A. felina to identify and annotate the CsC biosynthetic gene cluster. The only previously characterized gene cluster for the biosynthesis of similar compounds is that of the related immunosuppressant drug cyclosporine A (CsA). The CsA and CsC gene clusters share a high degree of synteny and sequence similarity. Amino acid changes in the adenylation domain of the CsC nonribosomal peptide synthase's sixth module may be responsible for the substitution of L-threonine compared to L-α-aminobutyric acid in the CsA peptide core. This screening strategy promises to yield additional antifungal natural products with a focused spectrum of antimicrobial activity.
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Xu, Lijian, Yan Li, John B Biggins, Brian R Bowman, Gregory L Verdine, James B Gloer, J Andrew Alspaugh, Gerald F Bills, et al. (2018). Identification of cyclosporin C from Amphichorda felina using a Cryptococcus neoformans differential temperature sensitivity assay. Applied microbiology and biotechnology, 102(5). pp. 2337–2350. 10.1007/s00253-018-8792-0 Retrieved from https://hdl.handle.net/10161/17693.
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Scholars@Duke
James Andrew Alspaugh
The focus of my research is to understand the ways in which microorganisms sense and respond to changes in their environment. As microbial pathogens enter the infected host, dramatic genetic and phenotypic events occur that allow these organisms to survive in this harsh environment. We study the model fungal organism Cryptococcus neoformans to define signal transduction pathways associated with systemic fungal diseases. This pathogenic fungus causes lethal infections of the central nervous system in patients with AIDS and other immunological disorders. In addition to being an important pathogen, C. neoformans displays well-characterized and inducible virulence determinants. It is an outstanding system for dissecting the signaling pathways associated with pathogenicity.
The main techniques used in the lab are those of molecular genetics. We are able to readily mutate C. neoformans genes by homologous recombination. Mutant strains with disruptions in targeted genes are then evaluated in vitro for various phenotypes including altered expression of polysaccharide capsule and melanin. The effects of gene disruption on pathogenicity are also evaluated in animal models of cryptococcal disease. Using these techniques, we have identified a novel G-alpha protein/cAMP-dependent signaling pathway associated with mating and pathogenicity.
This research is complemented by the other investigators in the Duke University Mycology Research Unit. The members of this research community are pursuing studies in fungal pathogenesis, identifying novel antifungal drug targets, and studying the ecology of several medically important fungi.
Keywords: Microbial Pathogenesis
Cryptococcus neoformans
Signal transduction
Fungal mating
G proteins
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