Redox properties and evolution of human glutaredoxins

Area of Science:

• Biochemistry
• Molecular Biology
• Evolutionary Biology

Background:

• Glutaredoxins (Grxs) are essential glutathione-dependent oxidoreductases within the thioredoxin superfamily.
• They catalyze thiol-disulfide exchange reactions utilizing active site cysteine residues.
• Human dithiol glutaredoxins feature a characteristic C-X-Y-C active site motif.

Purpose of the Study:

• To determine the redox potentials of human glutaredoxin 1 (hGrx1) and human glutaredoxin 2 (hGrx2).
• To identify and characterize non-active site disulfide bonds in human glutaredoxins.
• To perform a phylogenetic analysis of human glutaredoxins to understand their evolutionary roles.

Main Methods:

• Redox buffers, protein-protein equilibrium, and thermodynamic linkage were employed to determine redox potentials.
• Redox buffers and chemical digestion were used to identify non-active site disulfides.
• Phylogenetic analysis was conducted on all human glutaredoxins.

Main Results:

• The redox potentials for hGrx1 and hGrx2 were measured at -232 mV and -221 mV, respectively.
• A stabilizing non-active site disulfide bond (Cys28-Cys113) was identified in hGrx2, increasing protein stability by approximately 5 kcal mol(-1).
• Phylogenetic analysis revealed three distinct groups: Grx1, Grx2, and the conserved monothiol Grx5, with Grx1 and Grx2 diverging early in animal evolution.

Conclusions:

• The identified non-active site disulfide in hGrx2 is conserved in deuterostomes and likely stable under most in vivo conditions.
• Human glutaredoxins can be classified into three evolutionary groups based on their active site sequences and phylogenetic relationships.
• The study provides insights into the structural stability and evolutionary history of human glutaredoxins.