The alteration of the C‐terminal region of human frataxin distorts its structural dynamics and function

Abstract

Friedreich's ataxia (FRDA) is linked to a deficiency of frataxin (FXN), a mitochondrial protein involved in iron-sulfur cluster synthesis. FXN is a small protein with an a/b fold followed by the C-terminal region (CTR) with a nonperiodic structure that packs against the protein core. In the present study, we explored the impact of the alteration of the CTR on the stability and dynamics of FXN. We analyzed several pathological and rationally designed CTR mutants using complementary spectroscopic and biophysical approaches. The pathological mutation L198R yields a global destabilization of the structure correlating with a significant and highly localized alteration of dynamics, mainly involving residues that are in contact with L198 in wild-type FXN. , which is closely related to the FRDA-associated mutant FXN 81-193, conserves a globular shape with a native-like structure. However, the truncation of the CTR results in an extreme alteration of global stability and protein dynamics over a vast range of timescales and encompassing regions far from the CTR, as shown by proton-water exchange rates and 15 N-relaxation measurements. Increased sensitivity to proteolysis, observed in vitro for both mutants, suggests a faster degradation rate in vivo, whereas the enhanced tendency to aggregate exhibited by the truncated variant may account for the loss of functional FXN, with both phenomena providing an explanation as to why the alteration of the CTR causes FRDA. These results contribute to understanding how stability and activity are linked to protein motions and they might be useful for the design of target-specific ligands to control local protein motions for stability enhancement.

Friedreich Ataxia: current status and future prospects

“…The mature protein consists of amino acids 81–210 [9]. The structure is characterized by an α/β fold followed by the C-terminal region (CTR) with a nonperiodic structure that packs against the protein core [53]. Its impact on cellular function and survival is impressively reflected by early embryonic lethality in FXN knock-out mice [54].…”

Human Frataxin Folds Via an Intermediate State. Role of the C-Terminal Region

“…In particular, we have focused on mutations located in the CTR. We have observed that deletion of the CTR produces a complete alteration of hFXN internal dynamics and yields a critical destabilization of the protein (Δ G ° NU = 1.0 kcal mol − 1 for the truncated variant 19 20 ), suggesting why the closely related FRDA-associated mutant hFXN81-193 causes the disease 24 . In the case of hFXN90-195, ∼10% of the molecules are in the unfolded state at room temperature 20 .…”

“…1A ). hFXN is a very stable protein (∼9 kcal/mol − 1 19 20 ). Native state dynamics of hFXN has been deeply studied by NMR 19 21 in a broad range of timescales and also by molecular dynamics simulations (MDs 19 20 ).…”

“…hFXN is a very stable protein (∼9 kcal/mol − 1 19 20 ). Native state dynamics of hFXN has been deeply studied by NMR 19 21 in a broad range of timescales and also by molecular dynamics simulations (MDs 19 20 ). A number of FRDA-associated mutants were studied and characterized from the point of view of their effects on thermodynamic stability, internal dynamics and biological activity 3 16 21 22 .…”

Epigenetic regulation of clinical manifestations of Friedreich's disease

“…Фратаксин представляет собой белок (23 кДа), состоящий из 81-210 аминокислотных остатков, локализованный в митохондриальном матриксе и связанный с внутренней мембраной митохондрий [4]. Фратаксин играет важную роль в обмене железа и формировании железосерных кластеров, защите клетки от окислительного стресса, регуляции энергетического обмена, кальциевого и нейротрансмиттерного гомеостаза, поддержании мембранного потенциала, участвует в аксональном транспорте и фолдинге нейрональных белков.…”