Fetuin B

Fetuin-B (FETUB), a second member of the fetuin family in mammals, is also known as Fetuin-like protein IRL685, 16G2 and Gugu, which is expressed in liver and testis and contains 2 cystatin fetuin-B-type domains. FETUB is a protease inhibitor required for egg fertilization. FETUB is also required to prevent premature zona pellucida hardening before fertilization, probably by inhibiting the protease activity of ASTL, a protease that mediates the cleavage of ZP2 and triggers zona pellucida hardening (By similarity). As a liver-derived plasma protein, FETUB is essential for fertilization.