title: Human Frataxin Folds Via an Intermediate State. Role of the C-Terminal Region.
abstract: The aim of this study is to investigate the folding reaction of human frataxin, whose deficiency causes the neurodegenerative disease Friedreich's Ataxia (FRDA). The characterization of different conformational states would provide knowledge about how frataxin can be stabilized without altering its functionality. Wild-type human frataxin and a set of mutants, including two highly destabilized FRDA-associated variants were studied by urea-induced folding/unfolding in a rapid mixing device and followed by circular dichroism. The analysis clearly indicates the existence of an intermediate state (I) in the folding route with significant secondary structure content but relatively low compactness, compared with the native ensemble. However, at high NaCl concentrations I-state gains substantial compaction, and the unfolding barrier is strongly affected, revealing the importance of electrostatics in the folding mechanism. The role of the C-terminal region (CTR), the key determinant of frataxin stability, was also studied. Simulations consistently with experiments revealed that this stretch is essentially unstructured, in the most compact transition state ensemble (TSE2). The complete truncation of the CTR drastically destabilizes the native state without altering TSE2. Results presented here shed light on the folding mechanism of frataxin, opening the possibility of mutating it to generate hyperstable variants without altering their folding kinetics.
authors: Instituto de Química y Físico-Química Biológicas, Universidad de Buenos Aires, Junín 956, 1113AAD, Buenos Aires, Argentina.
authors: Santiago E
authors: SE
authors: Faraj
authors: Instituto de Química y Físico-Química Biológicas, Universidad de Buenos Aires, Junín 956, 1113AAD, Buenos Aires, Argentina.
authors: Rodolfo M
authors: RM
authors: González-Lebrero
authors: Instituto de Química y Físico-Química Biológicas, Universidad de Buenos Aires, Junín 956, 1113AAD, Buenos Aires, Argentina.
authors: Ernesto A
authors: EA
authors: Roman
authors: Instituto de Química y Físico-Química Biológicas, Universidad de Buenos Aires, Junín 956, 1113AAD, Buenos Aires, Argentina.
authors: Javier
authors: J
authors: Santos
mesh_terms: D002942:Circular Dichroism; D005621:Friedreich Ataxia / Q000378:metabolism; D006801:Humans; D033862:Iron-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D000072417:Protein Domains; D055550:Protein Stability; D017433:Protein Structure, Secondary; D058767:Protein Unfolding; D011994:Recombinant Proteins; D012965:Sodium Chloride / Q000737:chemistry; D014508:Urea / Q000737:chemistry; D000096923:Frataxin
chemical_list: D033862:Iron-Binding Proteins; D011994:Recombinant Proteins; D012965:Sodium Chloride; D014508:Urea; D000096923:Frataxin