Thioredoxin domain-containing protein 9 is a protein that in humans is encoded by the TXNDC9 gene. The protein encoded by this gene is a member of the thioredoxin family. The exact function of this protein is not known but it is associated with cell differentiation. Significantly diminishes the chaperonin TCP1 complex ATPase activity, thus negatively impacts protein folding, including that of actin or tubulin.