Spectroscopic Examination of the Electron Transfer Step for E.coli [2Fe-2S] Cluster Biosynthesis
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Date
2021-11-30
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Abstract
The excursion into biological iron-sulfur cluster assembly began at the close of the 20th century, and has continued to develop in the last twenty years. Currently, it is known that [2Fe-2S] clusters are assembled through the work of a cysteine desulfurase, which liberates sulfur from cysteine that is subsequently transferred to a scaffold protein housing iron, where electrons are then transferred to complete the [2Fe-2S] cluster. This system has been researched at length and tremendous progress has been made to uncover finer details of this process. However, gaps in knowledge still remain, primarily concerning the source of electrons and the mechanism by which they are donated to complete cluster assembly. A small [2Fe-2S] redox protein, ferredoxin, has been postulated to be the biological reductant, but evidence that conclusively establishes its behavior in this role is minimal. In spite of this, it has oft been cited as the definitive reductant for this process. To address this dearth in the field, spectroscopic techniques were employed in the E.coli model to assess the behavior of this ferredoxin (Fdx). UV-Visible spectroscopic assays reveal that the mechanism of electron donation from Fdx touted in the field is not catalytically competent for iron-sulfur cluster assembly, as a previously unexplored lag phase in redox activity was uncovered. With further excursions incorporating circular dichroism spectroscopy, Fdx is affirmed to serve as a physiological reductant. The results obtained challenge previously proposed facets of its behavior and shed light on its activity within in vitro settings, while also exploring the possibility of a secondary reductant at play in the cellular antioxidant glutathione.
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iron-sulfur clusters, iron-sulfur cluster biosynthesis, ferredoxin, spectroscopy, redox proteins, E. coli,