Conformational and functional similarities between glutaredoxin and thioredoxins.

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Abstract
The tertiary structures of thioredoxin from Escherichia coli and bacteriophage T4 have been compared and aligned giving a common fold of 68 C alpha atoms with a root mean square difference of 2.6 A. The amino acid sequence of glutaredoxin has been aligned to those of the thioredoxins assuming that glutaredoxin has the same common fold. A model of the glutaredoxin molecule was built on a vector display using this alignment and the T4 thioredoxin tertiary structure. By comparison of the model with those of the thioredoxins, we have identified a molecular surface area on one side of the redox‐active S‐S bridge which we suggest is the binding area of these molecules for redox interactions with other proteins. This area comprises residues 33‐34, 75‐76 and 91‐93 in E. coli thioredoxin; 15‐16, 65‐66 and 76‐78 in T4 thioredoxin and 12‐13, 59‐60 and 69‐71 in glutaredoxin. In all three molecules, this part of the surface is flat and hydrophobic. Charged groups are completely absent. In contrast, there is a cluster of charged groups on the other side of the S‐S bridge which we suggest participates in the mechanisms of the redox reactions. In particular, a lysine residue close to an aromatic ring is conserved in all molecules.