http://www.creativebiomart.net/description_382675_12.htm

BMPR1B(bone morphogenetic protein receptor, type IB,,His&GST-tagged), also known as ALK6, is a a member of the bone morphogenetic protein (BMP) receptor family of transmembrane serine/threonine kinases. It contains 1 GS domain and 1 protein kinase domain. In the chick embryo, it has been shown that BMPR1B is found in precartilaginous condensations. BMPR1B is the major transducer of signals in these condensations. On ligand binding, it forms a receptor complex consisting of two type II and two type I transmembrane serine/threonine kinases. Type II receptors phosphorylate and activate type I receptors which autophosphorylate, then bind and activate SMAD transcriptional regulators. BMPR1B also is a receptor for BMP7/OP-1 and GDF5. The BMPR1B receptor plays a role in the formation of middle and proximal phalanges. Defects in BMPR1B are the cause of acromesomelic chondrodysplasia with genital anomalies and brachydactyly type A2.