QSOX1

Quiescin sulfhydryl oxidase 1 is an enzyme that in humans is encoded by the QSOX1 gene.

This gene encodes an enzyme that is localized primarily to the Golgi apparatus and secreted fluids. QSOX1 is a multi-domain disulfide catalyst. Unlike other disulfide catalysts, QSOX1 can both generate disulfides de novo and catalyze dithiol/disulfide exchange. The de novo disulfide bond formation is catalyzed by the ERV1 domain that contains a FAD co-factor that allows depositions of electrons onto the terminal electron acceptor, typically molecular oxygen. The dithiol/disulfide exchange is catalyzed by the thioredoxin domain. The two domains are linked together by a flexible linker that allows the thioredoxin domain to first interact with the substrate protein and then regenerate by ERV1 domain.

QSOX1 gene expression is induced as fibroblasts begin to exit the proliferative cycle and enter quiescence, suggesting that this gene plays an important role in growth regulation. In fibroblasts QSOX1 is required for normal incorporation of laminin into the extracellular matrix, and thereby for normal cell-cell adhesion and cell migration.

Two transcript variants encoding two different isoforms have been found for this gene. The two isoforms have different tissue distribution and in addition isoform 1 has a transmembrane helix in the carboxy terminal while isoform 2 is a secreted soluble protein.