Metamorphic protein IscU alternates conformations in the course of its role as the scaffold protein for iron-sulfur cluster biosynthesis and delivery

► IscU is a metamorphic protein that converts between two folds: S and D. ► IscU adopts the D-state when interacting with IscS to pick up sulfur. ► Holo-IscU adopts the S-state, which is recognized by HscB. ► HscA:ATP does not bind IscU, but HscA:ADP binds the D-state of IscU. ► Conversion of IscU from the S- to the D-state leads to cluster release and delivery.