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Protein Expr Purif. 2010 Oct;73(2):161-6. doi: 10.1016/j.pep.2010.05.003. Epub 2010 May 13.

Of the vulnerability of orphan complex proteins: the case study of the E. coli IscU and IscS proteins.

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MRC National Institute for Medical research, The Ridgeway, London NW7 1AA, UK.


IscS and IscU, the two central protein components of the iron sulfur cluster assembly machinery, form a complex that is still relatively poorly characterized. In an attempt to standardize the purification of these proteins for structural studies we have developed a protocol to produce them individually in high concentration and purity. We show that IscS is a rather robust protein as long as it is produced in a PLP loaded form and that this co-factor is essential for fold stability and enzyme activity. In contrast to previous evidence, we also propose that, in contrast with previous evidence, IscU is a thermodynamically stable protein with a well defined fold but, when produced in isolation, is a 'complex-orphan protein' that is prone to unfolding if not stabilised by a co-factor or a protein partner. Our work will facilitate further structural and functional studies of these proteins and eventually lead to a better understanding of the whole machinery.

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