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Human mitochondrial glutaredoxin 2 (GLRX2), which controls intracellular redox balance and apoptosis, exists in a dynamic equilibrium of enzymatically active monomers and quiescent dimers. Crystal structures of both monomeric and dimeric forms of human GLRX2 reveal a distinct glutathione binding mode and show a 2Fe-2S-bridged dimer. The iron-sulfur cluster is coordinated through the N-terminal active site cysteine, Cys-37, and reduced glutathione. The structures indicate that the enzyme can be inhibited by a high GSH/GSSG ratio either by forming a 2Fe-2S-bridged dimer that locks away the N-terminal active site cysteine or by binding non-covalently and blocking the active site as seen in the monomer. The properties that permit GLRX2, and not other glutaredoxins, to form an iron-sulfur-containing dimer are likely due to the proline-to-serine substitution in the active site motif, allowing the main chain more flexibility in this area and providing polar interaction with the stabilizing glutathione. This appears to be a novel use of an iron-sulfur cluster in which binding of the cluster inactivates the protein by sequestering active site residues and where loss of the cluster through changes in subcellular redox status creates a catalytically active protein. Under oxidizing conditions, the dimers would readily separate into iron-free active monomers, providing a structural explanation for glutaredoxin activation under oxidative stress.

Original publication

DOI

10.1074/jbc.M608179200

Type

Journal article

Journal

J Biol Chem

Publication Date

02/02/2007

Volume

282

Pages

3077 - 3082

Keywords

Amino Acid Sequence, Binding Sites, Crystallization, Crystallography, X-Ray, Dimerization, Glutaredoxins, Glutathione, Glutathione Disulfide, Humans, Iron-Sulfur Proteins, Isoenzymes, Mitochondria, Molecular Sequence Data, Oxidoreductases, Protein Structure, Secondary, Recombinant Proteins, Sequence Alignment, Sequence Homology, Amino Acid