Radically Different Thioredoxin Domain Arrangement of ERp46, an Efficient Disulfide Bond Introducer of the Mammalian PDI Family

The mammalian endoplasmic reticulum (ER) contains a diverse oxidative protein folding network in which ERp46, a member of the protein disulfide isomerase (PDI) family, serves as an efficient disulfide bond introducer together with Peroxiredoxin-4 (Prx4). We revealed a radically different molecular architecture of ERp46, in which the N-terminal two thioredoxin (Trx) domains with positively charged patches near their peptide-binding site and the C-terminal Trx are linked by unusually long loops and arranged extendedly, forming an opened V-shape. Whereas PDI catalyzes native disulfide bond formation by the cooperative action of two mutually facing redox-active sites on folding intermediates bound to the central cleft, ERp46 Trx domains are separated, act independently, and engage in rapid but promiscuous disulfide bond formation during early oxidative protein folding. Thus, multiple PDI family members likely contribute to different stages of oxidative folding and work cooperatively to ensure the efficient production of multi-disulfide proteins in the ER. [Display omitted] •Crystal structures of the N-terminal two Trx domains of ERp46 were solved•SAXS analysis revealed an opened V-shape formed by three Trx domains in ERp46•Independent actions of ERp46 Trx domains on folding substrates were indicated•Different roles of ERp46 and PDI in oxidative protein folding are suggested Kojima et al. reveal a V-shape structure of ERp46, a disulfide introducer of the mammalian PDI family. The remarkably different thioredoxin domain arrangement and redox active-site location in ERp46 and PDI likely explain why these two PDI-family members play distinct roles during oxidative protein folding.