TMX4 is a member of the disulfide isomerase (PDI) family of endoplasmic reticulum (ER) proteins that catalyze protein folding and thiol-disulfide interchange reactions. TMX4 has an N-terminal ER-signal sequence, a catalytically active thioredoxin domain, one transmembrane domain and C-terminal ASP/GLU-rich calcium binding domain. Unlike most members of this family, it lacks a C-terminal ER-retention sequence. TMX4 has been shown to have reductase activity in vitro. [provided by RefSeq, Jan 2017] [taken from NCBI Entrez Gene (Gene ID: 56255)]. [taken from the Universal Protein Resource (UniProt) www.uniprot.org/uniprot/Q9H1E5].