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Conformational stability, dynamics and function of human frataxin: Tryptophan side chain interplay

This work analyzes three frataxin variants in which one tryptophan was replaced by a glycine: W155G, W168G and W173G. As expected, given its localization in the assembly site, W155G was not able to activate the desulfurase activity of the supercomplex for iron-sulfur cluster assembly. In turn, W168G, which was significantly more unstable than W155G, was fully active. W173G, which was highly unstable as W168G, showed a significantly decreased activity, only slightly higher than W155G. As W168G and W173G were highly sensitive to proteolysis, the authors investigated the protein motions by molecular dynamic simulations. They observed that W173G may display altered motions at the Trp155 site. Furthermore, the analysis revealed a H-bond network in which Trp155 takes part, involving residues Gln148, Asn151, Gln153 and Arg165. The authors suggest that this motion modulation that specifically alters the population of different Trp155 rotamers can be directly transferred to the assembly site, altering the dynamics of the ISCU His137 key residue. This hypothesis was also contrasted by means of molecular dynamic simulations of frataxin in the context of the complete supercomplex. The authors propose that the supercomplex requires very definite motions of Trp155 to consolidate the assembly site.

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