title: Metamorphic protein IscU changes conformation by cis-trans isomerizations of two peptidyl-prolyl peptide bonds.
abstract: IscU from Escherichia coli, the scaffold protein for iron-sulfur cluster biosynthesis and transfer, populates two conformational states with similar free energies and with lifetimes on the order of 1 s that interconvert in an apparent two-state reaction. One state (S) is structured, and the other (D) is largely disordered; however, both play essential functional roles. We report here nuclear magnetic resonance studies demonstrating that all four prolyl residues of apo-IscU (P14, P35, P100, and P101) are trans in the S state but that two absolutely conserved residues (P14 and P101) become cis in the D state. The peptidyl-prolyl peptide bond configurations were determined by analyzing assigned chemical shifts and were confirmed by measurements of nuclear Overhauser effects. We conclude that the S ⇄ D interconversion involves concerted trans-cis isomerization of the N13-P14 and P100-P101 peptide bonds. Although the D state is largely disordered, we show that it contains an ordered domain that accounts for the stabilization of two high-energy cis peptide bonds. Thus, IscU may be classified as a metamorphic protein.
authors.affiliation: Graduate Program in Biophysics, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: Ziqi
authors.initials: Z
authors.lastname: Dai
authors.forename: Marco
authors.initials: M
authors.lastname: Tonelli
authors.forename: John L
authors.initials: JL
authors.lastname: Markley
mesh_terms: D029968:Escherichia coli Proteins / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D007536:Isomerism; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry*; D011392:Proline / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D029968:Escherichia coli Proteins; D007506:Iron-Sulfur Proteins; C411665:IscU protein, E coli; D010455:Peptides; D011392:Proline