Structure of a putative immature form of a Rieske-type iron-sulfur protein in complex with zinc chloride.

Iron-sulfur clusters are prosthetic groups of proteins involved in various biological processes. However, details of the immature state of the iron-sulfur cluster into proteins have not yet been elucidated. We report here the first structural analysis of the Zn-containing form of a Rieske-type iron-sulfur protein, PetA, from Thermochromatium tepidum (TtPetA) by X-ray crystallography and small-angle X-ray scattering analysis. The Zn-containing form of TtPetA was indicated to be a dimer in solution. The zinc ion adopts a regular tetra-coordination with two chloride ions and two cysteine residues. Only a histidine residue in the cluster-binding site exhibited a conformational difference from the [2Fe-2S] containing form. The Zn-containing structure indicates that the conformation of the cluster binding site is already constructed and stabilized before insertion of [2Fe-2S]. The binding mode of ZnCl2, similar to the [2Fe-2S] cluster, suggests that the zinc ions might be involved in the insertion of the [2Fe-2S] cluster. Iron–sulfur clusters are important cofactors involved in a wide range of protein functions, however, the incorporation of FeS clusters into proteins remains underexplored. Here, the authors report the crystal structure of a Zn-containing form of a Rieske protein, in which ZnCl2 binds in an FeS-binding site, representing a putative immature form of a Rieske protein prior to FeS insertion. [ABSTRACT FROM AUTHOR]