Twisted Gastrulation Protein (TSG) is a secreted BMP binding protein structurally related to the BMP antagonists Chordin and Noggin. TSG can inhibit BMP activity by binding directly to BMP proteins, and can act either as a BMP4 agonist or antagonist (depending on the specific biochemical environment) by binding to the BMP4/Chordin complex. Recombinant human TSG is a 199 amino acid 22.2 kDa protein containing the BMP/TGFβ binding portion of the full length TSG protein.