Fe-S cluster assembly: sulphur, iron and electrons

摘要

Iron sulfur [Fe-S] clusters are versatile cofactors utilized by proteins for diverse biological functions (electron transfer, radical generation, non redox catalysis, sensing,..) in all living organisms and their assembly is performed by complex biosyn-thetic machineries. In Escherichia coli the two main pathways are the so called Isc (iscRSUA-hscBA-fdx-iscX) and Suf (sufABCDSE) systems (1, 2). The latter is active under oxidative stress and iron deficiency conditions. In both cases inorganic sulfur is supplied by a cysteine desulfurase (IscS/SufS) to a scaffold protein (IscU/IscA/ SufA) where the nascent Fe-S cluster is built and then transferred to target proteins (Figure) (3). This process requires a source of electrons (Fdx/SufB?) as well as a nucleotidase (HscBA/SufBCD). The source of Fe is less well established. Recent characterization of the SufBCD complex demonstrated a complex organization with [Fe-S] cluster and flavin cofactors, suggesting a major role in several aspects of the process: iron and sulfur mobilization, electron transfer, cluster assembly and transfer (4). On this basis a new chemical mechanism of [Fe-S] cluster assembly and transfer by the SUF machinery can be proposed.