THIS APPLICATION HAS BEEN DIVIDED OUT OF INDIAN APPLICATION NO. 229/KOLNP/2005 Field of the Invention [001] The invention relates generally to excipients and agents which solubilize proteins. In particular, the invention relates to compositions for, and methods of, maintaining or increasing the solubility of a protein under various biochemical conditions. The invention also relates to methods of, and compositions for, resolubilizing a protein which has precipitated out of solution. In a particular aspect, the invention relates to compositions for, and methods of, maintaining or increasing the solubility of proteins that belong to the transforming growth factor-b (TGF-b) superfamily. Background of the Invention [002] The TGF-b superfamily consists of more than 25 different signaling proteins found in both vertebrates and invertebrates. Protein members of the TGF-b superfamily influence a wide range of biological processes including cell growth, cell growth inhibition, tissue repair, cell differentiation, apoptosis, establishment of the dorso-ventral embryo body axis, and secretion of extracellular matrix components (Ebendal et a/. 1998, Journal of Neurosdence 51:139). Thus, members of the TGF- b superfamily provide attractive targets for the development of pharmaceutical agonists and antagonists that may be used to treat a wide variety of human diseases and conditions which are affected by the activity of one or more of the superfamily members. For example, antagonists and agonists of TGF-b superfamily members have practical application in the area of tissue repair and regeneration as well as in the area of differentiation of pluripotent stem cells into cells or tissues of a preferred lineage. Additionally, TGF-ft superfamily members also provide targets for gene therapy. The cloning and expression of many members of the family has been described. (See e.g. U.S. Patent Nos. 4,877,864; 5,108,922; 5,013,649; 5,116,738; 5,106,748; 5,187,076; -1A- 5,141,905; 5,688,678; 5,661,007; 5,637,480; 5,639,638; 5,658,882; and 5,635,372). [003] Among the members of the TGF-b superfamily are the bone morphogenetic proteins (BMP). BMPs were initially identified as regulators of cartilage and bone formation. Subsequent work has shown that BMPs, like other TGF-b superfamily members, play a role in many different biological processes including embryogenesis and morphogenesis of a variety of organs and tissues. Additionally, BMPs play a role in the growth, differentiation, and chemotaxis of several different cell types such as hematopoietic cells, epithelial cells, mesenchymal cells, and neuronal cells (Reddi, 1998, Nature Biotechnology 16:247; Ebendal, supra). [004] BMPs, like other members of the TGF-b superfamily are highly conserved across different animal species. The mature human BMP-2, for example, is completely homologous with mouse and rat BMP-2. The biologically active form of BMP-2 is a homodimer consisting of a disulfide linked carboxy terminal domain of 114 amino acids. BMP-2 exerts its affect on target cells by binding to a cell surface receptor comprised of a hetero- oligomer. The receptor is a complex of two serine/threonine kinase receptors (see Ebendal, supra; Reddi supra). [005] The human homolog of BMP-2 has been cloned, Wozney, 1989, Prog. Growth Factor Res. 1(4):267. Recombinant human BMP-2 can be expressed as a fragment of the full length BMP-2 consisting of either amino acids 266-396 or 283-396. The fragments form both homodimers and heterodimers resulting in six different isoforms. The six dimeric isoforms are denoted: 0°C and <65°C. In one embodiment the method of the invention is practiced at a temperature of 20°C. In another embodiment the method of the invention is practiced at a temperature of 4°C. In yet another embodiment, the method of the invention is practiced at a temperature of 37°C. [048] The method of the invention can be practiced at any pH so long as the method results in increased solubility of a protein of interest when contacted with a peptide comprised of SEQ ID NO:1, or a fragment thereof, as compared to the solubility of said protein of interest that is not contacted with a peptide comprised of SEQ ID N0:1, or a fragment thereof. Alternatively, the method of the invention can be practiced at a pH that results in the resolubilization of a protein of interest when contacted with a peptide comprised of SEQ ID NO:1, or a fragment thereof. Thus, in one embodiment the method of the invention can be practiced at a pH between >1 and <7.5. In another embodiment the method of the invention is practiced at physiological pH. In yet another embodiment the invention is practiced at a pH of 4.5. [049] Any concentration of the peptide comprised of SEQ ID NO: 1, or a fragment thereof, can be used in the practice of the methods of the -15- invention so long as the method results in increased solubility of a protein of interest when contacted with a peptide comprised of SEQ ID NO:1, or a fragment thereof, as compared to the solubility of said protein of interest that is not contacted with a peptide comprised of SEQ ID NO:1, or a fragment thereof. Alternatively, any concentration of the peptide comprised of SEQ ID NO:1, or a fragment thereof, can be used in the practice of the methods of the invention so long as the method results in the resolubilization of a protein of interest when contacted with a peptide comprised of SEQ ID NO:1, or a fragment thereof. In one embodiment the method of the invention is practiced with a peptide comprised of SEQ ID NO:1, or fragment thereof, at a concentration in the range of 1-1,000 nanomoles. In another embodiment the method of the invention is practiced with a peptide comprised of SEQ ID NO:1, or fragment thereof, at a concentration in the range of 1 -1,000 micromoles. In another embodiment the method of the invention is practiced with a peptide comprised of SEQ ID NO:1, or fragment thereof, at a concentration in the range of 1-1,000 millimoles. In another embodiment the method of the invention is practiced with a peptide comprised of SEQ ID NO:1, or fragment thereof, at a concentration in the range of 1-1,000 moles. [050] The method of the invention involves contacting a protein of interest with a peptide comprised of SEQ ID NO:1, or fragment thereof, wherein said peptide or fragment thereof, increases the solubility of the protein of interest or resolubilizes the protein of interest. In one aspect of the invention, the method of the invention is practiced with a peptide comprised of SEQ ID NO:1, or fragment thereof, that is present at a molar excess compared to the protein of interest. The peptide can be present at a molar excess, compared to the protein of interest, in the range of 1-1000-fold molar excess. In another aspect of the invention the method of the invention is practiced with the protein of interest present at a molar excess compared to the peptide comprised of SEQ ID NO:1, or a fragment thereof. The protein of interest can be present at a molar excess, compared to the peptide comprised -16- of SEQ ID N0:1, or a fragment thereof, in the range of 1-1000-fold molar excess. In one embodiment the method of the invention is practiced with a peptide comprised of SEQ ID NO:1, or fragment thereof, that is present at a 10-20 fold molar excess compared to the protein of interest. [051 ] Other than in the operating example, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches. [052] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. One of skill in the art will appreciate that any numerical value, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. [053] The following examples illustrate, but are not intended to limit, the scope of the invention. Example 1: Solubility of the Six Isoforms of rhBMP-2 [054] rhBMP-2 is produced in CHO cells and contains six dimeric isoforms