A stabilized variant activin receptor IIB

An isolated protein comprising a polypeptide IIB stabilized activin receptor, wherein said polypeptide is selected from the group consisting of: (a) a polypeptide consisting of the sequence set forth in the group consisting of SEQ ID NO: 4, 6, 12 and 14; (B) a polypeptide having at least 90% sequence identity with (a), wherein the polypeptide has W or Y at the position corresponding to position 28 of SEQ ID NO: 2 and T in position corresponding to position 44 of SEQ ID NO: 2, wherein the polypeptide is capable of binding myostatin, activin a or GDF-11, and (c) polypeptides having at least 95% sequence identity with ( a) wherein the polypeptide has W or Y corresponding to position 28 of SEQ ID NO position 2 and T corresponding to position 44 of SEQ ID NO position: 2, wherein the polypeptide He is capable of binding myostatin, activin a or GDF-11.