protein TGF-beta-like cystine-knot cytokine A protein with a core domain composition consisting of a signal peptide, a variable propeptide region and a Transforming growth factor beta like domain (Pfam:PF00019), which is a cystine-knot domain containing four conserved beta strands, S1-S4, which form two antiparallel beta sheets (SI-S2 and S3-S4) interconnected by three disulfide bridges in a knot-like topology. Cystines [II-V] and [III-VI] form a ring through which the remaining disulfide bond (Cys[I-IV]) penetrates. Insertion of different variable regions into this common motif has given rise to various subclasses of the growth factor cystine-knot domain. Category=family. TGF-beta superfamily protein PIRSF:PIRSF800009 PR:000000008