Aspergillus flavus squalene synthase as an antifungal target: Expression, activity, and inhibition

Junfeng Song, Na Shang, Noman Baig, Jiaqi Yao, Christopher Shin, Boo Kyun Kim, Qian Li, Satish R. Malwal, Eric Oldfield, Xinxin Feng, Rey Ting Guo

Research output: Contribution to journalArticlepeer-review


Invasive aspergillosis (IA) is a life-threatening disease impacting immunocompromised individuals. Standard treatments of IA, including polyenes and azoles, suffer from high toxicity and emerging resistance, leading to the need to develop new antifungal agents with novel mechanisms of action. Ergosterol biosynthesis is a classic target for antifungals, and squalene synthase (SQS) catalyzes the first committed step in ergosterol biosynthesis in Aspergillus spp. making SQS of interest in the context of antifungal development. Here, we cloned, expressed, purified and characterized SQS from the pathogen Aspergillus flavus (AfSQS), confirming that it produced squalene. To identify potential leads targeting AfSQS, we tested known squalene synthase inhibitors, zaragozic acid and the phosphonosulfonate BPH-652, finding that they were potent inhibitors. We then screened a library of 744 compounds from the National Cancer Institute (NCI) Diversity Set V for inhibition activity. 20 hits were identified and IC50 values were determined using dose-response curves. 14 compounds that interfered with the assay were excluded and the remaining 6 compounds were analyzed for drug-likeness, resulting in one compound, celastrol, which had an AfSQS IC50 value of 830 nM. Enzyme inhibition kinetics revealed that celastrol binds to AfSQS in a noncompetitive manner, but did not bind covalently. Since celastrol is also known to inhibit growth of the highly virulent Aspergillus fumigatus by inhibiting flavin-dependent monooxygenase siderophore A (SidA, under iron starvation conditions), it may be a promising multi-target lead for antifungal development.

Original languageEnglish (US)
Pages (from-to)517-523
Number of pages7
JournalBiochemical and Biophysical Research Communications
Issue number3
StatePublished - May 7 2019


  • Antifungal
  • Aspergillosis
  • Celastrol
  • Compound screening
  • Inhibition
  • Squalene synthase

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology


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