Activin receptor polypeptides variants and uses thereof

An isolated protein comprising a receptor polypeptide variant activin IIB (vActRIIB), wherein said polypeptide is selected from the group consisting of: (a) a polypeptide having the polypeptide sequence set forth in SEQ ID NO: 18 except by a single amino acid substitution at position 28, wherein the substitution is selected from any one of e by a, F, Q, V, I, L, M, K, H, W and Y; (B) a polypeptide having the polypeptide sequence set forth in amino acids 19 to 134 of SEQ ID NO: 18, except for a single amino acid substitution at position 28, wherein the substitution is selected from any one of E by A, F, Q, V, I, L, M, K, H, W and Y; (C) a polypeptide having the polypeptide sequence set forth in amino acids 23 to 134 of SEQ ID NO: 18, except for a single amino acid substitution at position 28, wherein the substitution is selected from any one of E by A, F, Q, V, I, L, M, K, H, W and Y; (D) a polypeptide having the polypeptide sequence set forth in amino acids 25 to 134 of SEQ ID NO: 15 18, except for a single amino acid substitution at position 28, wherein the substitution is selected from any one of E by A, F, Q, V, I, L, M, K, H, W and Y; (E) a polypeptide having at least 90% identity to any one of (a) to (d), wherein the substitution at position 28 is selected from any one of E by A, F, Q, V , I, L, M, K, H, W and Y, and wherein the polypeptide is capable of binding myostatin, activin a or GDF-11.