Single-Molecule Force Spectroscopy Reveals that the Fe-N Bond Enables Multiple Rupture Pathways of the 2Fe2S Cluster in a MitoNEET Monomer.

The mitochondrial outer membrane protein, mitoNEET (mNT), is an iron-sulfur protein containing an Fe2S2(His)1(Cys)3 cluster with a unique single Fe-N bond. Previous studies have shown that this Fe(III)-N(His) bond is essential for metal cluster transfer and protein function. To further understand the effect of this unique Fe-N bond on the metal cluster and protein, we used atomic force microscopy-based single-molecule force spectroscopy (AFM-SMFS) to investigate the mechanical unfolding mechanism of an mNT monomer, focusing on the rupture pathway and kinetic stability of the cluster. We found that the Fe-N bond was the weakest point of the cluster, the rupture of which occurred first, and could be independent of the cluster break. Moreover, this Fe-N bond enabled a dynamic and labile iron-sulfur cluster, as multiple unfolding pathways of mNT with a unique Fe2S2(Cys)3 intermediate were observed accordingly.