Reversible sequestration of active site cysteines in a 2Fe-2S-bridged dimer provides a mechanism for glutaredoxin 2 regulation in human mitochondria.
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.
Johansson
Catrine
C
Structural Genomics Consortium, Botnar Research Centre, University of Oxford, Oxford OX3 7LD, United Kingdom.
Kavanagh
Kathryn L
KL
Gileadi
Opher
O
Oppermann
Udo
U
D000595:Amino Acid Sequence; D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D019281:Dimerization; D054477:Glutaredoxins; D005978:Glutathione / Q000378:metabolism; D019803:Glutathione Disulfide / Q000378:metabolism; D006801:Humans; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism*; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology*; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
C516008:GLRX2 protein, human; D054477:Glutaredoxins; D007506:Iron-Sulfur Proteins; D007527:Isoenzymes; D011994:Recombinant Proteins; D010088:Oxidoreductases; D005978:Glutathione; D019803:Glutathione Disulfide