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Challenge: Fraxatin Challenge

Dataset description: public

Variant data: public

Dataset availability: public

Last updated: 14 April 2018

This his challenge will tentatively close at 9:00 PM PST (Pacific Standard Time) on 18 Apr 2018.

Download answer key and predictions: registered users only, limited by CAGI Data Use Agreement. The answer key and predictions are accessible to registered users only, and their use is limited by the CAGI Data Use agreement. Please log in to access the file.

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Frataxin is a highly conserved protein found in prokaryotes and eukaryotes that is required for efficient regulation of cellular iron homeostasis. Humans with a frataxin deficiency have the cardio- and neurodegenerative disorder Friedreich's Ataxia. A library of eight missense variants was assessed by near and far-UV circular dichroism and intrinsic fluorescence spectra to determine thermodynamic stability at different concentration of denaturant. These data were used to calculate a ΔΔGH20 value, the difference in unfolding free energy ΔΔGH20 between the variant and wild-type proteins for each variant. The challenge is to predict ΔΔGH20 for each frataxin variant.


The human frataxin is a protein localized in the mitochondrion and cytoplasm that promotes the heme biosynthesis and assembly and repair of iron-sulphur clusters by delivering Fe2+ to proteins involved in these pathways. The protein may play a role in protection against iron-catalyzed oxidative stress through its ability to catalyze the oxidation of Fe2+ to Fe3+. The oligomeric form but not the monomeric form of the protein has ferroxidase activity in vitro. Oligomerization may provide a mechanism by which the protein stores large amounts of iron in the form of a ferrihydrite mineral.

Reduced expression of frataxin is the cause of Friedreich's Ataxia (FRDA), a lethal neurodegenerative disease. According to SwissVar database, eight single amino acids variants (p.Leu106Ser, p.Asp122Tyr, p.Gly130Val, p.Ile154Phe, p.Trp155Arg, p.Arg165Cys, p.Leu182Phe and p.Leu198Arg) have been associated to FRDA (Corey, 2016). The role of frataxin in cancer is still ambiguous: studies have shown that frataxin protects tumor cells against oxidative stress and apoptosis, but also acts as a tumor suppressor. (Schulz et al., 2006; Guccini et al., 2011)

The single amino acid variants included in the Frataxin challenge were selected from the COSMIC (Catalog of Somatic Mutations in Cancer) database. These are somatic variants associated with neoplastic diseases and/or detected in cancer tissues. From the 21 variants reported in COSMIC we included in this challenge those that could be obtained as a soluble recombinant protein in E. coli, and excluded the variants whose expression failed.

The results of previous thermodynamic experiments on the wild-type and a different set of mutated human frataxin have been reported. (Faraj et al., 2016)


Human frataxin variants are obtained with specific mutagenesis primers by PCR, using wild-type protein as a template. Wild-type and mutants are then expressed in E. coli and purified. The structural conformation of the variants is compared to that of the wild-type by monitoring the near and far-UV circular dichroism and intrinsic fluorescence spectra. The thermodynamic stability is measured at a different concentration of denaturant (Urea) by monitoring the spectral changes (far-UV circular dichroism and intrinsic fluorescence emission) induced by urea. The spectral changes are fitted to zero denaturant concentration (ΔG H20).

Prediction challenge

For each variant, participants are asked to predict the ΔΔGH20 value, which is the difference in unfolding free energy (ΔGH20) between the mutant and wild-type proteins, in kcal/mol. The predictions will be evaluated via several methods including those that consider the difference between the predicted and experimental ΔΔGH20 values. In addition, predictions will be evaluated by dividing the variants into two classes: the significantly destabilizing mutants with ΔΔGH20 ≤ -1.0 kcal/mol, and the neutral/stabilizing mutants with ΔΔGH20 > -1.0 kcal/mol..

Prediction submission format

The prediction submission is a tab-delimited text file. Organizers provide a template file, which must be used for submission. In addition, a validation script is provided, and predictors must check the correctness of the format before submitting their predictions. Each data row in the submitted file must include the following columns:

In the template file, cells in columns 2-4 are marked with a "*". Submit your predictions by replacing the "*" with your value. No empty cells are allowed in the submission. For a given subset, you must submit predictions and standard deviations for all or none of the variants; if you are not confident in a prediction for a variant, enter an appropriate large standard deviation for the prediction. Optionally, enter a brief comment on the basis of the prediction. If you do not enter a comment on a prediction, leave the "*" in those cells. Please make sure you follow the submission guidelines strictly.

In addition, your submission should include a detailed description of the method used to make the predictions, similar to the style of the Methods section in a scientific article. This information must be submitted as a separate file.

To submit predictions, you need to create or be part of a CAGI User group. Submit your predictions by accessing the link "All submission forms" from the front page of your group. For more details, please read the FAQ page.

Additional information

The function of the human Frataxin and other information are reported in UniProt and are accessible with the identifier Q16595 (FRDA_HUMAN).

The structure of human Frataxin from position 90 to 208 has been determined by X-ray crystallography and is available from the PDB with code 1EKG.


Corey DR. 2016. Synthetic nucleic acids and treatment of neurological diseases. JAMA Neurol 73:1238-1242. doi:10.1001/jamaneurol.2016.2089

Faraj SE, Gonzalez-Lebrero RM, Roman EA, Santos J. 2016. Human frataxin folds via an interme-diate state. Role of the c-terminal region. Sci Rep 6:20782. PMCID:PMC4746760. doi:10.1038/srep20782

Guccini I, Serio D, Condo I, Rufini A, Tomassini B, Mangiola A, Maira G, Anile C, Fina D, Pallone F, Mongiardi MP, Levi A, Ventura N, Testi R, Malisan F. 2011. Frataxin participates to the hypox-ia-induced response in tumors. Cell Death Dis 2:e123. PMCID:PMC3101705. doi:10.1038/cddis.2011.5

Schulz TJ, Thierbach R, Voigt A, Drewes G, Mietzner B, Steinberg P, Pfeiffer AF, Ristow M. 2006. In-duction of oxidative metabolism by mitochondrial frataxin inhibits cancer growth: Otto war-burg revisited. J Biol Chem 281:977-981. doi:10.1074/jbc.M511064200


This challenge will be assessed by Emidio Capriotti, University of Bologna, Italy.

Download dataset: Fraxatin_dataset.txt (3.5 KB)

Download submission template: Fraxatin_submission_template.txt

Download submission validation script: Validation perl script

Dataset providers

The dataset is provided by the group of Roberta Chiaraluce and Valerio Consalvi, Sapienza University, Roma, Italy.

Revision history

30 Nov 2017 (v01): initial release

24 Sep 2018 (v02): Dataset availability added