ERP44 is a multifunctional endoplasmic reticulum (ER) chaperone that mediates thiol-dependent protein retention and quality control in the early secretory pathway 1. It forms mixed disulfides with substrate proteins through its conserved CRFS motif, functioning as a key player in "redoxtasis" alongside ER oxidoreductases 2. ERP44 cycles between the ER and Golgi compartments, controlling localization of enzymes lacking suitable retention signals and patrolling secretion of disulfide-linked oligomeric proteins, including adiponectin complexes 31. Its activity is regulated by zinc and pH gradients, with Golgi-resident ZnT transporters tuning ERp44's client-binding and release capacity 4. Beyond quality control, ERP44 inhibits calcium channel activity of the ryanodine receptor RyR2 through redox-sensitive association, with disease-relevant implications in cardiac arrhythmias where Ero1α-mediated dissociation of ERp44 from RyR2 promotes proarrhythmic calcium release 5. ERp44 also regulates selective ER retention of receptor tyrosine kinases during ER stress, competing with PDIA6 to control recovery kinetics 6. In cancer cells, ERp44 inhibition triggers Death Receptor oligomerization and apoptosis 7. Clinical relevance extends to pre-eclampsia, where elevated placental ERp44 expression correlates with altered renin-angiotensin signaling and reduced zinc availability 8.