Frataxin is a kinetic activator of the mitochondrial supercomplex for iron-sulfur cluster assembly. With the aim of creating new molecular tools to study this metabolic pathway, and ultimately, to explore new therapeutic strategies, the authors have investigated the possibility of obtaining small proteins exhibiting a high affinity for frataxin. In this study, the ribosome display approach, using human frataxin as the target was applied. The investigators focused on Affi_224, one of the proteins that were selected after five rounds of selection. The interaction between both proteins was studied and some applications of this specific molecular tutor, concerning the modulation of the supercomplex activity are discussed. Affi_224 and frataxin showed a KD value in the nanomolar range, as judged by surface plasmon resonance analysis. Most likely, it binds to the frataxin acidic ridge, as suggested by the analysis of chemical shift perturbations (NMR) and computational simulations. Affi_224 was able to increase Cys NFS1 desulfurase activation exerted by the FRDA frataxin variant G130V. Importantly, Affi_224 interacts with frataxin in a human cellular model. These results suggest quaternary addition may be a new tool to modulate frataxin function in vivo. Nevertheless, more functional experiments under physiological conditions should be carried out to evaluate Affi_224 effectiveness in FRDA cell models.

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