Structural and thermodynamic characterization of the adrenodoxin-like domain of the electron-transfer protein Etp1 from Schizosaccharomyces pombe

The protein Etp1 of Schizosaccharomyces pombe consists of an amino-terminal COX15-like domain and a carboxy-terminal ferredoxin-like domain, Etp1 fd, which is cleaved off after mitochondrial import. The physiological function of Etp1 fd is supposed to lie in the participation in the assembly of iron–sulfur clusters and the synthesis of heme A. In addition, the protein was shown to be the first microbial ferredoxin being able to support electron transfer in mitochondrial steroid hydroxylating cytochrome P450 systems in vivo and in vitro, replacing thereby the native redox partner, adrenodoxin . Despite a sequence similarity of 39% and the fact that fission yeast is a mesophilic organism, thermodynamic studies revealed that Etp1 fd has a melting temperature more than 20 °C higher than adrenodoxin. The three-dimensional structure of Etp1 fd has been determined by crystallography. To the best of our knowledge it represents the first three-dimensional structure of a yeast ferredoxin. The structure-based sequence alignment of Etp1 fd with adrenodoxin yields a rational explanation for their observed mutual exchangeability in the cytochrome P450 system. Analysis of the electron exchange with the S. pombe redox partner Arh1 revealed differences between Etp1 fd and adrenodoxin, which might be linked to their different physiological functions in the mitochondria of mammals and yeast. The crystal structure of S. pombe Etp1 fd, a ferredoxin involved in the mitochondrial assembly of iron–sulfur clusters, is presented. We describe the structural, thermodynamic and functional properties of Etp1 fd in comparison with bovine Adx, a ferredoxin active in mitochondrial P450 systems. [Display omitted]