High-Level Soluble Expression of Recombinant Human Bone Morphogenetic Protein-2 in <i>Escherichia coli</i>

Human Bone Morphogenetic Protein-2 (hBMP-2) serves as a critical regulator in bone and cartilage formation; however, its industrial application is hindered by its inherent tendency to form inclusion bodies in prokaryotic expression systems. To address this issue, we established a recombinant hBMP-2 (rhBMP-2) expression system using the pCold II plasmid and the SHuffle T7 strain. We explored several strategies to enhance the solubility of rhBMP-2, including coexpression with molecular chaperones, vesicle-mediated secretory expression, fusion expression with synthetic intrinsically disordered proteins (SynIDPs), and fusion expression with small-molecule peptide tags. Our results showed that coexpression with the molecular chaperone pGro7 significantly improved the solubility of rhBMP-2. Fusion with SynIDPs led to complete solubility of rhBMP-2; however, the protein was expressed exclusively in the monomeric form. Among the tested small-molecule peptide tags, GB1 was the most effective, achieving fully soluble rhBMP-2 expression. Western blot analysis confirmed the coexistence of monomeric and dimeric forms of rhBMP-2. Subsequent purification of rhBMP-2 through metal chelate chromatography resulted in an expression level of 109.7 ± 5.0 mg·L^-1. In summary, we successfully demonstrated fully soluble expression of rhBMP-2 in <i>Escherichia coli</i>, providing a valuable foundation for its industrial-scale production.