Soluble Expression of Recombinant Human Bone Morphogenetic Protein-7 (rhBMP-7) in Escherichia coli Using SUMO Fusion System

BMPs belong to transforming growth factor β superfamilies, which their principal role is inducing bone and cartilage formation at heterotopic and orthotopic sites. Since the formation of inclusion bodies is the main limitation of producing these proteins in Escherichia coli, in this study, the small ubiquitin-like modifiers (SUMO) fusion system was employed to improve solubility and expression of recombinant human BMP-7 (rhBMP-7) in E. coli. The SUMO fusion system has the ability to enhance protein expression, reduce target protein proteolytic degradation, and increase protein folding and solubility. In the current study, the SUMO protein gene was fused to the N-terminus of the BMP-7 gene, and cloned in the pET-28a vector. After purification of the expressed SUMO-BMP-7 protein by Ni-NTA chromatography, SUMO was removed from the BMP-7 protein using SUMO protease. In the second step of purification using Ni-NTA chromatography, the cleaved BMP-7 protein was purified and then identified by Western blot analysis. The results of the current study demonstrated that the SUMO fusion system is able to increase the soluble form of rhBMP-7. Furthermore, rhBMP-7 can be purified by a two-step purification strategy including: 1) purification of SUMO-BMP-7 and 2) purification of rBMP-7 after cleavage using Ni-NTA chromatography. Altogether, this research has provided a feasible approach for large-scale production of soluble rhBMP-7, to facilitate its further medical development.