Structure and function of protein disulfide isomerase

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The formation of disulfide bonds in many secretory proteins represents an essential step in their folding and maturation, and protein disulfide isomerase (PDI) is the key enzyme required for disulfide bond formation. It oxidizes two cysteine residues in newly synthesized proteins to form a disufide bridge and also catalyzes the isomerization of incorrectly formed disulfide linkages in proteins containing three or more cysteine residues. Our initial crystal structure of PDI revealed that the two catalytically competent (a and a’) and two inactive (b and b’) thioredoxin-like domains are arranged in the shape of the letter “U”. The active sites in the a and a’ domains are located on opposite ends of the “U” with a large substratebinding cleft located between them, and the b and b’ domains form the base of the “U”. A subsequent lower resolution structure demonstrated large-scale conformational changes. Through a combination of biochemical, biophysical and structural studies we will study the contribution of domain motions to the catalytic activity of PDI, analyze the interaction of the enzyme with different substrates and its redox partner Ero1, structurally characterize mammalian PDI to rationalize variations of the catalytically active domains in and between species, and we will also determine structures with inhibitors to further refine the catalytic mechanism and as a starting point for rational drug design.