Department of Pediatric & Adolescent Medicine, Mayo Clinic, Rochester, Minnesota, USA.
Metallomics. 2017 Jun 21;9(6):773-801. doi: 10.1039/c7mt00089h.
Early studies of the bacterial Fe-S cluster assembly system provided structural details for how the scaffold protein and the cysteine desulfurase interact. This work and additional work on the yeast and human systems elucidated a conserved mechanism for sulfur donation but did not provide any conclusive insights into the mechanism for iron delivery from the iron donor, frataxin, to the scaffold. We previously showed that oligomerization is a mechanism by which yeast frataxin (Yfh1) can promote assembly of the core machinery for Fe-S cluster synthesis both in vitro and in cells, in such a manner that the scaffold protein, Isu1, can bind to Yfh1 independent of the presence of the cysteine desulfurase, Nfs1. Here, in the absence of Yfh1, Isu1 was found to exist in two forms, one mostly monomeric with limited tendency to dimerize, and one with a strong propensity to oligomerize. Whereas the monomeric form is stabilized by zinc, the loss of zinc promotes formation of dimer and higher order oligomers. However, upon binding to oligomeric Yfh1, both forms take on a similar symmetrical trimeric configuration that places the Fe-S cluster coordinating residues of Isu1 in close proximity of iron-binding residues of Yfh1. This configuration is suitable for docking of Nfs1 in a manner that provides a structural context for coordinate iron and sulfur donation to the scaffold. Moreover, distinct structural features suggest that in physiological conditions the zinc-regulated abundance of monomeric vs. oligomeric Isu1 yields [Yfh1]·[Isu1] complexes with different Isu1 configurations that afford unique functional properties for Fe-S cluster assembly and delivery.
早期对细菌 Fe-S 簇组装系统的研究提供了支架蛋白和半胱氨酸脱硫酶相互作用的结构细节。这项工作以及对酵母和人类系统的进一步研究阐明了硫供体的保守机制，但并没有为铁从铁供体 frataxin 到支架的传递机制提供任何确凿的见解。我们之前表明，寡聚化是酵母 frataxin (Yfh1) 可以在体外和细胞内促进 Fe-S 簇合成核心机制组装的一种机制，在这种机制中，支架蛋白 Isu1 可以与 Yfh1 结合，而无需存在半胱氨酸脱硫酶 Nfs1。在这里，在没有 Yfh1 的情况下，发现 Isu1 存在两种形式，一种主要是单体，具有有限的二聚倾向，另一种具有强烈的寡聚倾向。虽然单体形式被锌稳定，但锌的缺失会促进二聚体和更高阶寡聚体的形成。然而，在与寡聚 Yfh1 结合后，两种形式都呈现出相似的对称三聚体构象，使 Isu1 的 Fe-S 簇配位残基与 Yfh1 的铁结合残基非常接近。这种构象适合 Nfs1 的对接，为铁和硫向支架的协调捐赠提供了结构背景。此外，独特的结构特征表明，在生理条件下，单体与寡聚 Isu1 的锌调节丰度产生具有不同 Isu1 构型的 [Yfh1]·[Isu1] 复合物，为 Fe-S 簇组装和传递提供独特的功能特性。
