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PDIb family, ERp44 subfamily, first redox inactive TRX-like domain b; ERp44 is an endoplasmic reticulum (ER)-resident protein, induced during stress, involved in thiol-mediated ER retention. It contains an N-terminal TRX domain with a CXFS motif followed by two redox inactive TRX-like domains, homologous to the b and b' domains of PDI. Through the formation of reversible mixed disulfides, ERp44 mediates the ER localization of Ero1alpha, a protein that oxidizes protein disulfide isomerases into their active form. ERp44 also prevents the secretion of unassembled cargo protein with unpaired cysteines. ERp44 also modulates the activity of inositol 1,4,5-triphosphate type I receptor (IP3R1), an intracellular channel protein that mediates calcium release from the ER to the cytosol. Similar to PDI, the b domain of ERp44 is likely involved in binding to substrates.
Jiyao W et al.(2023). "The conserved domain database in 2023.",