Project Summary: Members of the thioredoxin superfamily of proteins are found in large numbers in all organisms. These proteins perform a variety of reactions, including formation of protein disulfide bonds, reduction and isomerization of disulfide bonds, destruction of peroxides and others. The purpose of this project is to undertake a comprehensive study of these proteins and the proteins they interact with in the model organism, Escherichia coli. We will study the folding of these proteins, their mechanism of action, and how their substrate specificity is determined. The studies will focus on the protein DsbA, which makes disulfide bonds in proteins, on the thioredoxins and glutaredoxins, which reduce disulfide bonds in proteins, and on a peroxiredoxin, AhpCF, which destroys peroxides. We will also characterize suppressor mutations that restore growth to strains that are missing cytoplasmic members of the thioredoxin family which perform reductive reactions. Such studies have allowed and will allow us to identify additional proteins that carry out disulfide bond reduction or other physiological pathways that interact with these reducing proteins. In the case of DsbA, we will determine how this enzyme recognizes cysteines in substrate proteins and chooses those that it will join in a disulfide bond. For the thioredoxins and glutaredoxins, through mutations that alter their specificity, we will explore how these proteins recognize their substrates, and identify new substrates. We will exploit a novel approach to protein folding to obtain a large collection of mutants that interfere with folding of thioredoxin and shed light on how this protein folds into its three-dimensional structure. Each component of this project has relevance to public health. Disulfide-bonded proteins such as peptide hormones (insulin, etc.), proteins used to treat heart condtions (tPA) and antibodies can be produced more cheaply and in high quantities through the genetic manipulation of E. coli. Our studies in the past have led to increased amounts of these proteins being produced in the bacteria. The thioredoxin and glutaredoxin reductants are important in biological processes that influence the development of diseases such as heart disease and cancer. Already, studies on this family of proteins in E. coli has provided basic knowledge that has led to a better understanding of those family members that are found in higher organisms, including humans.