XBP2, or X-box binding protein 1, is a human gene encoded by XBP1. It may also be known as: X-box-binding protein 1; TREB-5; XBP-1; Tax-responsive element-binding protein 5; TREB5. The encoded protein has an amino acid length of 261 and a mass of 28.7 kDa. XBP2 is a member of the BZIP family. Homologs of this gene exist in other organisms, including: Mouse, Rat, Zebrafish, Frog, Chicken.