Anatomy of an iron-sulfur cluster scaffold protein: Understanding the determinants of [2Fe–2S] cluster stability on IscU

• Published in: Biochimica et biophysica acta 2015-06, Vol.1853 (6), p.1448-1456
• Main Authors: Adrover, Miquel, Howes, Barry D., Iannuzzi, Clara, Smulevich, Giulietta, Pastore, Annalisa
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Circular Dichroism; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; Hydrophobic and Hydrophilic Interactions; Iron-Sulfur Proteins - chemistry; Iron-Sulfur Proteins - genetics; Iron-Sulfur Proteins - metabolism; Iron–sulfur cluster; isc operon; Models, Molecular; Molecular Sequence Data; Mutant Proteins - chemistry; Mutant Proteins - genetics; Mutant Proteins - metabolism; Mutation, Missense; Protein Binding; Protein Stability; Protein Structure, Tertiary; QM/MM methods; Scaffold protein; Sequence Homology, Amino Acid; Spectrum Analysis, Raman
• ISSN: 0167-4889; 0006-3002; 1879-2596
• DOI: 10.1016/j.bbamcr.2014.10.023

Protein-bound iron sulfur clusters are prosthetic groups involved in several metabolic pathways. Understanding how they interact with the host protein and which factors influence their stability is therefore an important goal in biology. Here, we have addressed this question by studying the determinants of the 2Fe–2S cluster stability in the IscU/Isu protein scaffold. Through a detailed computational study based on a mixed quantum and classical mechanics approach, we predict that the simultaneous presence of two conserved residues, D39 and H105, has a conflicting role in cluster coordination which results in destabilizing cluster-loaded IscU/Isu according to a ‘tug-of-war’ mechanism. The effect is absent in the D39A mutant already known to host the cluster more stably. Our theoretical conclusions are directly supported by experimental data, also obtained from the H105A mutant, which has properties intermediate between the wild-type and the D39A mutant. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases. •IscU is the scaffold protein involved in iron–sulfur cluster formation.•Conflicting interactions between cluster chelators determine cluster stability.•Cluster instability is necessary to release the cluster to further acceptors.