Reduction of mutant phage T4 glutaredoxins by Escherichia coli thioredoxin reductase

Fifteen mutant T4 glutaredoxins (previously T4 thioredoxin) have been assayed for activity with Escherichia coli thioredoxin reductase. The mutations include substitutions in the region of the active site, in the 2 cysteines, and in the 2 residues between the cysteines forming the active-site disulfide bridge. Mutant thioredoxins where substitutions have been made in charged residues around the active site show the biggest differences in activity. The positive residues Lys-13 and Lys-21 were found to be important for efficient binding to thioredoxin reductase. Substitution of the aspartic acid at position 80 with a serine produced a glutaredoxin with superior activity. This mutant glutaredoxin has earlier been shown to be more efficient than the wild type in thiol transferase activity (Nikkola, M., Gleason, F. K., Saarinen, M., Joelson, T., Björnberg, O., and Eklund, H. (1991) J. Biol. Chem. 266, 16105-16112). Even the glutaredoxin P66A, where the active-site cis-proline has been substituted, could be efficiently reduced by thioredoxin reductase. Glutaredoxins lacking one or both cysteines were not active.