Potent circulating inhibitor of angiogenesis (By similarity). Signals through the type I activin receptor ACVRL1 but not other Alks (PubMed:25751889). Signaling through SMAD1 in endothelial cells requires TGF-beta coreceptor endoglin/ENG (PubMed:23300529). Homodimer; disulfide-linked. Detected in extracellular fluid as mature homodimer, and in complex with its propeptide (By similarity). Interacts with ACVRL1, BMPR2 and ACVR2B with high affinity (in vitro) (PubMed:25751889). Identified in a complex with ACVRL1 and ACVR2B (By similarity). Has ten times lower affinity for ACVR2A (in vitro) (PubMed:25751889). Interacts with ENG, forming a heterotetramer with a 2:2 stoichiometry. Can form a heteromeric complex with ENG and ACVRL1 (By similarity). Interacts with type I receptor ACVR1 (By similarity). A reversible disulfide bond can be formed between the two subunits in the homodimer; this has no effect on GDF2 activity. Belongs to the TGF-beta family. Can promote osteogenic differentiation in vitro (PubMed:25751889). This is probably not physiologically relevant.