8.A.88.2.5
Thioredoxin-related transmembrane protein 1, TMX1, TMX, TXNDC, TXNDC1, UNQ235/PRO268, of 280 aas and 2 - 4 TMSs, one N-terminal, one C-terminal, and possibly 1 or 2 inbetween (Guerra and Molinari 2020). The ER of mammals contains more than 20 members of the Protein Disulfide Isomerase (PDI) family. These enzymes regulate formation, isomerization and disassembly of covalent bonds between cysteine residues. As such, PDIs ensure protein folding, which is required to attain functional and transport-competent structure, and protein unfolding, which facilitates dislocation of defective gene products across the ER membrane for ER-associated degradation (ERAD). The PDI family includes over a dozen soluble members and few membrane-bound ones. Among the latter are five PDIs grouped in the thioredoxin-related transmembrane (TMX) protein family (Guerra and Molinari 2020).