Unpublished draft

QSOX1

QSOX1 (quiescin sulfhydryl oxidase 1) is the secreted enzyme that inserts disulfide bonds into extracellular-matrix proteins — the oxidase that finishes folding collagen, laminin, and other matrix components after they leave the cell.

Function

QSOX1 catalyzes disulfide-bond formation using a thioredoxin domain to accept electrons from client-protein thiols, a shuttle domain to move them, and an FAD-dependent oxidase domain to hand them to oxygen. It is the only enzyme known to introduce disulfide bonds into proteins outside the cell and independent of the Ero1–PDI machinery of the ER. Its substrates are matrix and basement-membrane proteins, and its secretion is driven by quiescence