Structural domains comprising this superfamily share the structure of FIP-Fve (Fungal Immunomodulatory Protein Fve), a major fruiting body protein from Flammulina velutipes, a mushroom possessing immunomodulatory activity PMID:7705335. It is involved in several different processes including the stimulation lymphocyte mitogenesis, suppression of systemic anaphylaxis reactions and oedema, enhancement of the transcription of IL-2, IFN-gamma and TNF-alpha, and haemagglutination of red blood cells. It is believed to be a lectin with specificity for complex cell-surface carbohydrates.

Fve adopts a tertiary structure consisting of an immunoglobulin-like beta-sandwich, with seven strands arranged in two beta sheets, in a Greek-key topology. It forms a non-covalently linked homodimer and dimerisation occurs by 3-D domain swapping of the N-terminal helices and is mainly stabilised by hydrophobic interactions PMID:12948495.