High-throughput amenable fluorescence-assays to screen for calmodulin-inhibitors

Ganesh babu Manoharan, Kari Kopra, Ville Eskonen, Harri Härmä, Daniel Abankwa*

*Corresponding author for this work

Research output: Contribution to journalArticleResearchpeer-review

9 Citations (Scopus)


The KRAS gene is highly mutated in human cancers and the focus of current Ras drug development efforts. Recently the interface between the C-terminus of K-Ras and calmodulin (CaM) was proposed as a target site to block K-Ras driven cancer cell stemness. We therefore aimed at developing a high-throughput amenable screening assay to identify novel CaM-inhibitors as potential K-Ras stemness-signaling disruptors. A modulated time-resolved Förster resonance energy transfer (mTR-FRET)-assay was developed and benchmarked against an identically designed fluorescence anisotropy (FA)-assay. In both assays, two CaM-binding peptides were labeled with Eu(III)-chelate or fluorescein and used as single-label reporter probes that were displaced from CaM upon competitor binding. Thus, peptidic and small molecule competitors with nanomolar to micromolar affinities to CaM could be detected, including a peptide that was derived from the C-terminus of K-Ras. In order to detect CaM-residue specific covalent inhibitors, a cell lysate-based Förster resonance energy transfer (FRET)-assay was furthermore established. This assay enabled us to measure the slow, residue-specific, covalent inhibition by ophiobolin A in the presence of other endogenous proteins. In conclusion, we have developed a panel of fluorescence-assays that allows identification of conventional and covalent CaM-inhibitors as potential disruptors of K-Ras driven cancer cell stemness.

Original languageEnglish
Pages (from-to)25-32
Number of pages8
JournalAnalytical Biochemistry
Publication statusPublished - 1 May 2019
Externally publishedYes


  • Calmodulin
  • Cancer stemness
  • FRET
  • Fluorescence anisotropy
  • KRAS
  • Z′-factor


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