Stabilized receptor polypeptides and uses thereof

An isolated protein comprising a stabilized activin IIB receptor polypeptide (svActRIIB) wherein said polypeptide is selected from the group consisting of:

• (a) a polypeptide consisting of the sequence set forth in SEQ ID NO:
• 2, except for a single amino acid substitution at position 28, and a single amino acid substitution at position 44, wherein the substitution at position 28 is selected from the group consisting of W and Y, and the substitution at position 44 is T;
• (b) a polypeptide consisting of the sequence set forth in amino acids 19 through 134 of SEQ ID NO:
• 2, except for a single amino acid substitution at position 28, and a single amino acid substitution at position 44, wherein the substitution at position 28 is selected from the group consisting of W and Y, and the substitution at position 44 is T;
• (c) a polypeptide consisting of the sequence set forth in amino acids 23 through 134 of SEQ ID NO:
• 2, except for a single amino acid substitution at position 28, and a single amino acid substitution at position 44, wherein the substitution at position 28 is selected from the group consisting of W and Y, and the substitution at position 44 is T;
• (d) a polypeptide consisting of the sequence set forth in amino acids 25 through 134 of SEQ ID NO:
• 2, except for a single amino acid substitution at position 28, and a single amino acid substitution at position 44, wherein the substitution at position 28 is selected from the group consisting of W and Y, and the substitution at position 44 is T;
• (e) a polypeptide having at least 80% sequence identity to any one of (a) through (d), except for a single amino acid substitution at position 28, and a single amino acid substitution at position 44, wherein the substitution at position 28 is selected from the group consisting of W and Y, and the substitution at position 44 is T, wherein the polypeptide is capable of binding myostatin, activin A, or GDF-11.