The N-terminal order-disorder transition is a critical determinant for a metamorphosis of IscU

Abstract

IscU, a key scaffold protein mediating the biogenesis of iron-sulfur (Fe-S) clusters, exhibits metamorphic characteristics crucial for its versatile and efficient function. Previous studies have demonstrated that IscU has two interconverting conformations: the structured state (S-state) and the disordered state (D-state), each contributing to its distinct functionality and interaction network. Despite its physiological importance, the precise mechanism underpinning the maintenance of IscU's unique structural heterogeneity has remained elusive. In this study, we used computational, spectroscopic, and biochemical approaches to reveal that the Nterminal order-disorder plays a critical role in the metamorphic modulation of Escherichia coli IscU. With computational analysis, we found that the N-terminal region displays greater structural plasticity, which is linked to other regions of IscU through coevolutionary relationships. We also used site-directed mutagenesis, size-exclusion chromatography, circular dichroism, isothermal titration calorimetry, and nuclear magnetic resonance spectroscopic techniques to demonstrate that the degree of orderliness in the N-terminal region correlates positively with the stabilization of IscU's S-state and negatively with its affinity for HscA. Finally, we also showed that the peptide mimicking the N-terminal motif can modulate IscU's metamorphic properties. Our data indicate that the flexibility in the N-terminal region is finely tuned to optimize IscU's physiological efficiency and efficacy. Moreover, our study showcases important evidence suggesting a novel therapeutic potential of the Nterminus-like peptide for related pathogenic processes.