Acts as a bone morphogenetic protein (BMP) coreceptor (PubMed:18976966). Through enhancement of BMP signaling regulates hepcidin (HAMP) expression and regulates iron homeostasis (PubMed:18976966). Interacts with BMP2 and BMP4 (By similarity). Interacts with BMP6 (By similarity). Interacts with BMPR1B (PubMed:16604073). Interacts with TMPRSS6 (PubMed:18976966, PubMed:19357398). Also released in the extracellular space. Adult and fetal liver, heart, and skeletal muscle. Autocatalytically cleaved at low pH; the two chains remain linked via two disulfide bonds (PubMed:25156943). Also proteolytically processed by TMPRSS6, several fragments being released in the extracellular space; regulates HJV activity in BMP signaling and thefore iron homeostasis (PubMed:18976966, PubMed:25156943). The disease is caused by variants affecting the gene represented in this entry. Belongs to the repulsive guidance molecule (RGM) family.