WFIKKN proteins are secreted multidomain proteins containing a WAP (whey acidic protein)-, a follistatin/Kazal-, an immunoglobulin-, two Kunitz-type protease inhibitor-domains, and an NTR (netrin) domain. They have been reported to inhibit the activity of trypsin, and to bind GDF11 (growth and differentiation factor 11) and myostatin (GDF8). Due to the presence of multiple domains that frequently serve as protease inhibitors, WFIKKN proteins are presumed to control the action of diverse serine proteases as well as metalloproteinases.WFIKKN2 (also known as WFIKKNRP) expression in human is observed in ovary, testis, pancreas, brain and lung.