May be involved in redox reactions associated with the formation of disulfide bonds (By similarity). May contribute to the quality control of protein folding in the endoplasmic reticulum. May regulate protein folding by enhancing the catalytic activity of UGGT1/UGCGL1 and UGGT2/UGCGL2 (By similarity). Forms a tight complex with UGGT1/UGCGL1. Interacts with UGGT2/UGCGL2. Interacts with RDH11. The association with UGGT1/UGCGL1 is essential for its retention in the endoplasmic reticulum. Belongs to the selenoprotein M/F family.