The glutaredoxin -C-P-Y-C- motif: influence of peripheral residues.

The variety of cellular functions performed by proteins of the thioredoxin superfamily is made possible by the wide range of redox potential associated with their active site -Cys-X-X-Cys- motif. The determinants of these differences in redox potential are of considerable interest but are not well understood. E. coli Glutaredoxin 1 (Grx1) and 3 (Grx3) are important model systems with different redox properties, despite sharing the same -Cys-Pro-Tyr-Cys- motif, very similar overall structures, and 33% sequence identity. Very long molecular dynamics simulations (0.25 micros total) and electrostatic calculations provide a revised view of the reduced Grx1 active site, which now can be reconciled with biochemical and functional data. Comparison of this new model to Grx3 uncovers differences in the structure, dynamics, and electrostatics of these active sites. The influence of peripheral residues on the properties of the -Cys-X-X-Cys- motif is illustrated specifically with the effect of a Lys to Arg substitution.